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STRONGBACK DISCUSSION etc.
113 needs a new beam and since Ebb has broke the mold I think we're going to laminate a new beam similar to his. Fortunately for me, I have a friend that is well versed in the ways of wood. He's laminated everything from fishing nets to display cases to full blown foot bridges. He also finds my anxiety regarding this piece humorous. To him it's just another arc, but as we all know it's the backbone of our beloved little craft. So we've done some research and mixed his experience with a little nautical input. Here is where it has to end up. One of the previous owners did a repair(hack) job on the area NEAR the mast step but not really. As far as I can tell all they did was cut out the cabin liner in that area cut through the inner skin and then glue it back in completely cockeyed and unfair. Off by a strong 3/16":mad: Not to mention that the inner skin is still mobile under the step. So we'll put in our strongback and main bulkhead first and then go topside and finish the job.
p.s. I know-I know the plywood head liner doesn't look original. But it's stuck really well to the fiberglass so we'll deal with it. Actually it may facilitate in adding handholds forward.
strengthening the strongback
I was thinking of doing the repair recommended in the manual where you add steel plates to either side of the beam under the mast. Where I didn't see any bowing there before, or very little, it seems to be more pronounced now.
But I have lots of questions.
I guess I don't really understand why adding the plates would strengthen the strongback--they wouldn't really be resting on anything so they wouldn't actually bear any weight.
I met someone who did this on an Albin Vega but he recommended strongly that you not jack up the beam first, because of all the unknown stresses you might inadvertently add. He just added the plate to the beam as it was. Any opinions?
I pulled off some of the formica around the beam to see what was under there and I'd like to keep going with taking it off but it continues behind the lockers. Any suggestions for how to cut it flush with the top surface of the lockers? Also, I've been warned against doing this, the part I took off came off very easily but I guess if some of it is better adhered you could actually damage the bulkhead. Opinions?
also, I found three bolts already going through the beam--is that normal?
Robin
Mischief #44
Strengthening the mast support, strongbacks etc.
Thanks to Bill for your continuing efforts and to Dave (marymandara) for your efforts to discover and or produce masthead replacements and rudder shoes etc. Rather than respond on that thread in the "General - Off Topic" forum, I am asking for this new one on the topic of "Strengthening the mast support, strongbacks etc." in this "Technical forum"
My big technical problem right now is serious structural damage to the mast support area and strong back caused by a recent accident, and also a damaged mast head fitting. I have looked at the Association Manual and various threads on this site in regard to reinforcing or augmenting the strongback, and finding the necessary parts. The information seems to be spread all over, but the available information is incomplete.
I have found and reviewed photos of the main salon side of stainless steel plates added to the strongbacks in Sirroco and Orinoco Flow, but would be interested in shots of those installations from the forward cabin and also photos and text descriptions of approaches taken by others to deal with mast compression and mast support issues.
I had no personal issues in this area whatsoever, until two days ago, but in a harbor tabernacle-related accident on July 28th, my mast was driven downward and aft into the deck thus cracking the laminate or solid section under the mast clear through to the cabin liner. A previous owner unstepped the mast and modified the deck section with epoxy in time past in a manner which will not be clear to me until destructive testing has been initiated. I imagine that I may have my hands full shortly.
I have not been able to determine the extent of damage to the masthead fitting. It took the brunt of th eimpact, but transferred much of the force down the mast into the deck.
Just knowing that new mast head fittings may be available soon is very helpful to me.
I fear that the repairs may be both expensive and costly time-wise.
It would be nice to have all of this information in one thread on this forum. So if you all see fit, I could use some photos and words of advice in this area.
Commander Compression Post
The top plate/fitting for my compression post seems to be crushing as though the plate that is the bottom is being driven up into the fitting. Pictures when I get to the boat later this week.
I read the sections on compression posts but I am still not clear what I am dealing with in terms of removing/replacing what I have. I know that plate that the mast sits on was replaced by the former owner with one he had fabricated from a phenolic material similar to what has been use for blocks.
Oh well, all can't be bad. I put the first coat of varnish on my stripped and filled grabrails, and the Red Sox won behind Tim Wakefield on his birthday. This is Boston after all.;)
3 Attachment(s)
Clarification and strongback forensics
Again, the materials used in late-model "Katie Marie" prove to be different than that used in earlier boats...
Of course, she had no diagonal braces, so I am sure that that had an effect on what I see with her OEM strongback. Although it is *not* rotted, it *has* cracked (see pics, cracks are evident). Without diagonals, it was under more stress, I'm sure. Additionally, it is a solid 1/2" less in the vertical dimension than what ebb measured on his strongback (3.75" vs ebb's 4.25"), and only 1 3/4" wide (1" less than ebb's!) - so it is a significantly smaller beam. Yet she still sailed on for 40 years almost...
One thing I noticed, and mentioned before IIRC - the flexation (is that a word? it is now... :)) of the side decks, forward of the bulkhead, which resulted in some cracking of the inner deck skin there. I see no evidence of this cracking on the after side of the bulkhead. It is because of this evidence of force transmittal that I decided to go with the wider beam. I think it was point loading which was responsible for the cracking - the deck was trying to bend around the bulkhead. (!!!) So, to clarify what I think may be a misconception because I didn't clearly state it before: The width of my upcoming beam is only in the smaller part an attempt to make up for its reduced thickness; primarily, in my addled mind, the increased width is to spread loads across the structure while stiffening it to alleviate/cancel any torsional loads. Do dat make sense? :)
By way of explanation: I know that the beam will flex downward, even if only incrementally, when the boat is under strain of full sail and pounding into seas. Said bending will transfer the load out to the cabin trunk sides. Visualization: hold your hands, halfway cupped, fingertips touching at the top of a small arc, to simulate the arch shape of the inside of the cabin trunk. The mast sits on your fingertips. Imagine it pushing down, simulate it with your hands, you can see that it transfers that force out to the sides. End result: the cracking I see. A wide beam will spread that load across more surface area, which translates into more strength, and less of a load at any one point. Right? It will serve in a similar manner to do what the diagonals Katie never had would have done, had they been there.
*That's* why I want the width. Spreading the love... ;)
I'm not counting on the entirety of the strongback to support the mast, just a small part of it. I'll be supporting the mast in the vertical with 2 metal poles I will put roughly in place of the former doorway frame. The poles will contact the strongback beam and cabin sole on wide bases. Up top, under the mast, center-to-center of these bases will only be about 16", so the span which needs to be strong enough to resist the crushing force of the mast will be unsupported for less than 14".
I am still designing it in my mind, haven't yet settled on that which feels "right". I've been thinking 2" thick on the beam because I think that done properly it will be strong enough, as well as a being visually nice. I haven't ruled out a thicker spot in the beam under this area, tapered into the rest of the beam for visual flow and load-spreading. I suppose I also could go with a metal plate in this span area, and go even thinner on the beam, since it will be poles doing most of the work.
Last, I'd assemble the beam of vertically-aligned plywood pieces with resin *and* glass cloth between the layers of ply, like in my "boxes" drawing, not just resin or glue. By using plywood instead of foam for the core material, I think it should add strength/stiffness.
compression beam possible quick fix.
Hope that 'Bill Ariel 231' will post here. He is more practical and less wordy than I.
The support beam has a bow in it, of course, that more or less conforms to the curve of the coach roof. The support beam supports the composite fiberglass/balsa laminate that the mast step and mast sits on.
I believe that over time there is natural settling and shrinking that happens even though the wood of the beam is still in good condition. If you have opening across the top it may merely be a condition of age. Even bad original fitting that has opened even more.
Test the beam for soft spots especially in the center. If you have rot, that is a more complicated problem. It's another diagnosis. A repair such as described below cannot be fudged on a rotton beam. Replacement.
Check the curve of the roof outside to see if the mast rigging has pulled the mast into the roof any. Flattened it.
Because the navigation wires (used to) go into the interior through a hole under the hollow of the mast, rain water may have rotted the balsa under the mast-step in the composite. Check the roof if there is a slightly more localized depression. Needs to be fixed.
The coach roof should have a fair curve to it. Anything else requires a change in plan.
If you are lucky to have the mast sitting on a nice round cabin roof without any flattening (you may be the first!) then you can go about finding a way to fill the narrow space between the beam and the coach roof inside.
When you decide to go full monte on this fix, you remove the deck mast step by taking out the two 1/4" (#16) bronze flat-head lags that clamp it to the beam inside. Could be problem. When mine came out on 338 the cabin roof nearly returned to its original molded curve. And the narrow space inside opened up considerably more.
Pearson fudged the fit when assembling the Ariel as they used the mast support beam to clamp in the forward end of the cabin liner. That means that any fix cannot be attempted from the cabin - but from the V-berth area. It also supposes that the beam didn't fit quite as snug as it was supposed to. The beam may be tight against the liner on plywood bulkhead side but not quite so tight on the V-berth side.
You cannot fix the space problem with the mast rigged and pushing down on the roof. You can fix it when you RETURN THE COACH ROOF TO ITS ORIGINAL MOLDED CURVE by temporarily relieving all the pressures on it. The mast has to be taken down.
The coach roof has some rounded dimensions that isn't really compatible with flat carpentry.
Look at the problem with a few options in mind. You could for example bandsaw and shape to fit a single piece of wood that you glue into the space. That's the best way.
One uncommon way to consider.
Clean, scrape and remove paint, silicone snot, fillers that are in and around the space. You are working from the V-berth side. And you are deciding what you can do that will keep the roof totally supported.
I have had success using wood filler pieces and epoxy mishmash (laminating epoxy, fumed silica as thickener, and 1/4" chopped fiberglass strand) a kind of hairy pudding.
Wet the inside area with plain mixed epoxy and wipe it up best you can. Use terry toweling pieces stapled to thin battens. Get this 'primer/bond coat' dry as you can after wetting so that your mishmash won't mix with it and loosen and sag out of the joint.
Slide your wood filler pieces in slathered with gobs of pudding. You will have done a dry run so you know they fit good and where. The more wood, the less expensive glue. Longer pieces might even add a little strength to the beam.
Make sure you are stuffing the cavity all across the top.* You may be using some shim/wedges to get a tired coach roof to curve back properly - no forcing - you don't want to put anything under tension here - it will pull apart later - just enough.
I would shim the coach up using the beam in the center if necessary. Or prop the coach roof fair next to the beam with some 1X2 or 2X2 from the berth or sole. They'll be in the way, tho.
You might have a special shim or two that can be left epoxied in there. Use durable woods like fir and mahogany. Don't leave anything sticking out.
Once it's gooped and filled, take paper towels and remove any squeeze out and runs.
Clean up with alcohol so that there is minimal sanding prep for the next step.
This is a quick and dirty fix that allows the carpentry to be kept in place. It will only work if your diagnoses was correct.
Assumes that your beam and bulkhead are in good shape. That the composite under the mast is also OK. And the mast step itself.
It can be done this way, but I don't really recommend it. I would do a classic reconstruction if warrented - and do it right.
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* To control the extent of epoxy being pushed into and through the joint (the juices may run down the cabin side of the beam and bond the cabin door trim )- use cheap polyethylene foam 'backer rod' from your concrete store in the back of the space (seen from the V-berth). It isn't hard rod, it's soft yet firm foam you can stuff into tight places to create a dam. When you push in the wood filler pieces, you want the epoxy pudding to kind of billow out. There's going to be a little waste.
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BUT it's hard to know exactly what you got there without some photos. Good luck.
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Commander to Ariel conversion
The Commander has a compression post under the mast that transfers the load right to the keel. Only a knuckle head would want to change a strong and fool proof design like that!
I'm kinda a knuckle head.
In an attempt to create a roomy, private head with easy access I want to remove the compression post and put in a strongback, full bulkheads and a door like the Ariel. looking at the Ariel drawings I don't see how the load is carried to the keel. It appears that the bulkhead is relied on to carry and disperse the load. It looks like there is a vertical support on either side of the doorway, but I don't see anything under it. does it just terminate at the sole?
The manual (pg 23)shows diagonal supports, but does not show how they terminate on the lower end. Is there any additional structure not pictured in the drawings?
How thw strongback was installed in A338 by Pearson
C'227,
Nice to see those two compared in drawings with each other like that. Thanks.
You are correct on all points.
I've gone on about this subject adnauseum elsewhere. But suffice to say that in the Ariel the bulkhead is part of the mast support system. There are the two posts that define the doorway - they go down to the hull above the turn of the bilge (screwed to the plywood bulkhead.)
There are two cross braces on the Vberth side also screwed to the bulkhead that terminate on the Vberth plywood tops. And two more vertical braces that support the end of compression beam at the coachroof sides - also terminating on the Vberth. Across the top the compression beam is also screwed to the bulkhead. And held in place thru the top by two bronze #14s or #16s coming thru the mast pad, thru the composite deck, and into the beam.* All structural wood was white oak.
The plywood bulkhead in A338 is really two halves with a filler across the top of the doorway and a filler across at the step up into the V-berth stateroom. There is no work done by either of these fillers. (FYI A338 has since been remodeled to remove the doorway.)
The plywood "bulkhead" is tabbed to the hull ONLY
and not to the under deck or the coachroof sides or overhead.
Only the hull. And not across where one might expect a 'floor' to be in a wood boat - per your question.
Originally the space between the bulkhead and the liner was stuffed with a factory supplied fabric covered foam tape.
The compression beam load is ultimately taken to the hull via the half bulkheads (let's call them) on either side of the doorway. The compression beam is not supported in the center between the door posts. The door posts therefore are dual compression posts if you look at it that way. But they bear on the hull incidentally. In an upgrade a wider bearing pad would be cut in under these posts.
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*ANY upgrade or remodel imco, if you are working from the original Pearson model,
should have all dimensional wood members GLUED and screwed to the plywood at the very least.
But the Pearson model is very flawed.
Locking in the strongback
Been trying to see some progress in the A338 interior. (hopefully some pics in the Gallery soon)
So the anti-compression beam/struts and old ply glued in some time ago came into focus again.
What remaining of the original ply bulkhead: the pieces across the top that match the section of the beam and the skinnied down struts that terminate on the V-berth with the skinny remains of old ply have finally been mechanically connected with 24 #14 s.s. phillipshead screws. These are 316 flathead sheetmetal screws - meaning that the shank of the screw is like a straight lag - not tapered like wood screws. These 1/4" screws are indeed lags. (McMasterCarr.)
Worked out great. Since I was screwing into oak the pilothole could be tweeked a little wider so that the fastening was driven (with the Hitachi hammer drill) without fear of breaking. I'm wondering what kind of sheetmetal these screws would normally be used for?
BTW, would never use 316 screws in an exposed situation. Only bronze or monel should be used in oak. Wet oak eats iron for breakfast.
As back up for the laminated oak beam I choose 3/8" silicon bronze carriage bolts (Jamestown) with the bolthead inside and the nut buried in the deck composite. Drilled in 7 of these bolts along the length.
Began with a 1/4" hole drilled completely through.
Used a 1 3/4" holesaw to cut through the top into the balsa. The little lid popped off easy enough exposing the dry tunafish.
A 1/2" chisel quickly (almost TOO easily!!!) evacuated the wood. Used the same chisel to undercut the surrounding balsa. Put a tiny chunk of 1/4" dowel in the hole.
Then dumped two-part epoxy into the holes. Gratified to see very little liquid get absorbed and mopped it out with papertowels.
Refilled the holes with mishmash and came back later with the little PorterCable beltsander and knocked the hockypucks flat.
Then redrill the 1/4" hole.
Took a Bosch 1 1/8" flat bit with a large screw pilot. This sort of thing will want to take charge and pull the bit into the work. But I was using the screw thingy to center the bit in the hole - and bored down into the new puck enough to take a washer and a jamnut - together only 1/4" in depth. Plus a skoch for the fill to cover.
I'm going down today to the boat where I will drill the hole out to 3/8". I think I will prepare the square recess in the oak, knock the bolt thru, screw on the nut and see if the Fein tool* can pare the end of the bolt off right on top of the nut.
I'll refill the remaining hole with mishmash. let it set (hope the epoxy makes up for the skinny nut), dish it out a bit with the grinder and top it with a little circle of 6oz glass.
Then fair. Should be relatively seamless and never show up in the future.:o
The main reason for the bolts is that I don't trust epoxy used to laminate the beam. The bolts are not parallel to each other as each was drilled in perpendicular to the curve of the beam. In itself that's pretty strong - even if fastening through the deck, as described, is questionable.
Seems like the structure is locked.
Pity the poor sap what has to take this apart in the future!
If there is ever any question about the beam, it certainly seems possible to add an aluminum plate to the V-berth side of the beam. The plate would be cut to the exact shape of the beam and the coachroof.. Since the load is at right angle to any fastening, they could copy the same 'sheetmetal' screw as above with the plate also glued on with rubber adhesive, isolating the screws as well.
Driving screws into the thin oak laminations, therefore keep the screws relatively short.
If I were doing this again I would cut the beam out of solid white oak like the original. Could vertically laminate together thinner planks and thru-bolt.
AND as FRANK DURANT sez the beam could be vertically cut out of MERANTI HYDROTEC BS-1088 sheet and glued together (TiteBond III?). Could be curve laminated also, I guess. Since solid oak has no short grain like the cross layers in ply, I would definitely make the cross section of a meranti glue-up heftier than the oak dimensions.
BTW, only this plywood - NO OTHER, NO FIR, NO BIRCH - can be used for this purpose. imco
Hope this is useful.
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*Fein tool not so fine. Did nothing on the bolt ends. You can take a Fein to metal, but you can't make it cut.
I got a rant on this tool we'll save for later. Put a little flex cutoff blade in the Makita grinder and cut the bronze bolt ends like it was banana.
Resorcinol vs Epoxy / apples and oranges
Well,
Resorcinol is a wood specific 'bonder'.
If you were gluing exterior mahogany rails up from strips and scarf joints there is no other glue. When you glue coaming blocks and winch islands up with epoxy you will have separation at some point. And as I just said if you have an epoxy glue-up like a bowsprit and/or teak anchor roller they are guaranteed to come apart. I don't know how long it'll take, but the more heat and wet/dry cycles they experience the sooner they will come apart.
I'm talking about pieces of wood brought together into a structure.
Epoxy IS definitely more versatile. You can glue wood together and seal it with the same epoxy. You can fill gaps and fillet, you can laminate fiberglass onto wood and foam panels with the same stuff. You could probably do a barrier coat on the hull with it. But, by definition, you only achieve a mechanical bond.
I hesitate to use that term here as the adhesion is mechanical but not a BOND. There is no comparing here with Resorcinol which can only glue flat pieces of wood together FOREVER. It has a bad rap because of its short open time and need for high clamping and controlled temp.
If I had been more comfortable with Resorcinol I might have done A-338's strongback lamination with it. I felt I couldn't do it within the short open time required.
It is entirely possible to put together a new rudder for the Ariel/Commander with foam and glass OR plywood and glass using good epoxy. There is always the chance that the epoxy can separate from the wood or the foam.
You have to take this into account when designing the rudder. But this is not gluing wood-to-wood. The whole intent is to encapsulate the wood - and it sometimes doesn't work. Exposed, varnished wood swells and shrinks. Epoxy glue-line is more or less non-shrink and hard. Wood wins.
If you had to glue wood-to-wood together for underwater use (like the original non-encapsulated rudder) Nobody would spec epoxy. It's possible to butcher-block and pre-bond pieces together into 'planks' with Resorcinol for cutting the shape and use polyurethane or polyether for gluing/caulking edge to edge planks. Most people these days would then SEAL the wood with a thinned epoxy, then attempt to waterproof with a polyurethane coating (or whatever new comes down the everchanging chemical pike.) Or go right to bottom paint. Imco that's conventional wisdom.
In every case epoxy must be protected with another coating. Even a novolac needs UV protection. Pigmented epoxy coatings/paints will chalk and breakdown. There is no comparison with LPU coatings Even polyester coatings will outlast epoxy coatings. On those winch islands use a clear coating with the highest UV rating you can find. That'll help some.
The chemistry keeps changing. There are new combinations appearing: epoxy polyesters. epoxy urethanes and resorcinol epoxies, and ETC for both adhesives and coatings. Quite amazing.
But at the moment everyday epoxies that we buy really have limited use on the exterior of a cruising sailboat.
Please, I work with these assumptions on my Areil. If there are developments or stuff I've forgotten (more likely every day), please clue me and the boat in! We both depend on it.
The limited info about glues and coatings that I work with IS ALL conventional.
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google>
Laminating white oak w/ Resorcinol - The WoodenBoat Forum
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For unstressed gluing somebody by now must have tried using CLEAR polyether or a silyl-urethane. !NOT SILICONE! Also sold as Hybrid Sealant/adhesive.
This is a one-part, low odor, 100% solids, long life, moisture cured, always flexible synthetic rubber in a gun tube.
Worth experimenting - like gluing a stack of mahogany blocks together and boiling them for awhile!!!
Resorcinol vs epoxy - a small rant for those who are following through on the controv
google> Have epoxy adhesives improved recently - Sailing with Lin and Larry ...
www.landlpardey.com/Tips/2007/April.html
You can also find discussions on The WoodenBoat Forum
and the boat design forum.
The second site seems to be sat on by guys like me who dog onto every new post and subject. I have a problem with them because what they say, often with something off color, is hearsay and somebody else's opinion - not even their own. They're comedians. And always NOT funny. I don't go there anymore.
The WoodenBoat Forum seems more sane. Inquiries are often by first timers so the experts who answer are likely to be basic and simple.
On the designforum you will find those who put Larry down - for whatever reason.
Larry at one point took at least one epoxy manufacturer to task for making false claims about the product. You no longer will find data sheets that say the epoxy is waterproof. Or stable in a cruising environment.
Lin and Larry have built their own sailboats and taken them around the world. Larry is an amazing observer. With tens of thousands of cruising miles in wooden boats I'll take his prejudice on glues for gospel. They have received recognition and awards (for their convictions and courage I expect.)
I listen to them and ignore the jealous marina rats who can only put them down.
Both Resorcinol and epoxy have their limitations.
The first because it is a technical glue.
And epoxy because its versatility lulls people into ignoring its limits.
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We all labor with what we know - what we think we know - what we would like to know - with modern chemistry and with traditional ways of thinking and working, I don't believe any thread with prejudices and opinion is convincing.
So try this one on for size and follow it through to the end. It's on the www.woodenboat.com forum. And this is a "flog the dead horse" subject for many of these guys. This thread has a bunch of boat builders and amateurs talking about this subject. Not all the bases are covered but the thread is revealing and will help you come to an understanding of the problem.
google: White Oak glued with Epoxy, PL, Gorilla Glue, Resorcinal The....
(incluide the resorcinal (sic) misspelling.)
The thread begins with "few 3" post
Thanks Ebb but you had me convinced already...
My resorcinal will show up here Monday from Jamestown. ;)
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Commander strongback versus Ariel strongback
As I have mentioned before I plan to remove my commander compression post and replace it with a strongback. So today I started reading some of the prior posts to determine the demensions I should aim for on the strongback. Then I started measuring my commander and it seems that there are some differances between the the two boats in the amount of curvature of the deck unless I'm missing something else.
The drawing on page 23 of the manual shows the bottom of the strongback as a straight line from one side of the cabin to the other (or so I assume since the full width is not shown).
ebb said that his original strongback was 4-1/4" tall in the middle and tapering to 2-1/2" tall at the ends and 2-3/4" thick. If ebb's original was straight accross the bottom, that would indicate there was only 1-3/4" of camber from the edge of the cabin to the center.
ephifany said his original was only 3-3/4" tall in the middle but from the picture his does not look like it was flat on the bottom. So I may be making an assumption I should not.
In any case, I have 4" of camber in my deck. I placed a straight edge accross the cabin touching the bottom of the deck on each end and in the middle I had a rise of 4". So I will not be making my strongback straight across the bottom. If I want to end up someplace in the 2" thick area on the ends that means it would extend down 6" in the center. That is a bit much IMHO.
Below is a sketch of the approx. layout I'm looking to do. I plan to make it from 3ea. 4/4 boards of white oak laminated together vertically with resorcinol which will give me approx 2-3/4" thickness. I will butter the top of the strongback prior to putting it in place with thickened epoxy and then tab it to the deck and the bulkhead supporting it which will also be tabbed to the hull and deck. And of course I will have white oak bracing on the v-birth side which will be covered with 1/4' mahogany plywood as will the aft side of the bulkhead.
Any suggestions or comments about the plan?
support the load or spread the load
Sorry Jerry,
assume is the mother of all foul ups.
The key still is we can have nothing move under the mast.
And each of us has our own unique solution it seems when we stray from the box.
I love the sweet lines of the Commander.
The curve of the cabin roof is particularly pleasing.
Maybe, maybe it's possible to design a kind of 'break water across the cabin under the mast.
Have the beam outside.
If it wasn't a breakwater but a rounded slope sided and gel-coated mound it might just disappear and not mess with the lines.