Knotmeter Head Replacement Knot Fitting

[Bill]

Here’s the problem: The diameter of the replacement knotmeter's head unit is 5/8 of an inch larger than the hole for the one being replaced. In addition to the fact that I can’t find a 4-5/8 inch hole saw (4-1/2 or 4-3/4 seems to be the only sizes available), there is nothing into which I can drill a hole saw's pilot drill to keep the saw lined up over the old hole. Without the pilot drill, the saw just wants to bounce around, scraping up the paint on the bulkhead of the cabin trunk!

Ebb Borregaard to the rescue! After listening to my tail of woe, Ebb Borregaard suggested that I use the saw to cut a hole in a piece of scrap lumber and then place that piece of wood over the old hole to use as a saw guide.

Eureka! What a great idea. How come I didn’t think of that?

Using the 4-1/2 inch diameter saw, I cut a hole in a scrap of plywood. Next, I purchased two 3-1/2 inch wide "C" clamps with as deep a reach as I could find (that turned out to be 4-1/2 inches).

Here is the "custom hole drilling assembly:"

[Bill]

Here is the custom hole drilling assembly clamped to the outside of the cabin trunk’s bulkhead. [As you can see, the photo was taken after the job was completed, because I didn’t think about taking photos while the job was in progress. ]

[Bill]

Here is the clamped in place custom hole drilling assembly viewed from inside the cabin:

[Bill]

Removing the last 1/8-inch from the hole was accomplished with a rasp attachment on a portable drill. Fiberglass dust, of course, went everywhere.

At least there was no need to mess with the hole in the hull for the transducer. The replacement knot meter is the same brand (Signet) as before and both use the same transducer.

[ebb]

Bill,
Probably won't be doing that install again. EH?
But
for anybody else....
Lenox makes the best bi-metal blades anywhere.
They have a 4 3/4" (at www.coastaltool.com they get $32!*) Maybe need their arbor too.

Wouldn't that little bit of oversize worked ok?

*they have a 6" L. holesaw too. How'd you like to swing that one? It's a great way to tear your hand off at the wrist. Lenox doesn't seem to be as bad grabbing the work as some of the others - a lot of guys freehand these mothers. Plumbers, electricians, boat workers.

[mbd]

Nice work guys! Thanks for sharing that. Every task like this should be documented just so, so we invalids can learn learn learn. More fodder for the files! Thanks!

PS. Still waiting on the Gallery thread for Mai Kai - she seems like way too nice of a boat NOT to be displayed in one handy thread like Frank's or Kurt's. I hate to point this out, but Ebb's thread has gone a bit stale - is that because he's working on other people's boats lately and not his own?

[Bill]

PS. Still waiting on the Gallery thread for Mai Kai - she seems like way too nice of a boat NOT to be displayed in one handy thread like Frank's or Kurt's. I hate to point this out, but Ebb's thread has gone a bit stale - is that because he's working on other people's boats lately and not his own?

Maika'i is not nearly of the calabur of most boats in the gallery forum. Her skipper is a bit retarded when it comes to boat work -- which is why he pays Ebb the "big bucks" for advice. Mostly, we try to not come in last while racing . . .

As for Ebb's "stale" thread, it won't stop raining here in the Bay Area this Spring, so we can't take photos. The area is one day short of setting a new record for the most rainy days in March . . .

[Al Lorman]

Nice work, Bill. But there is another way. Clamp a solid peice of wood behind the existing hole, put a pilot hole in the center, then use a hole saw to cut the desired size hole.

[SkipperJer]

Sounds to me like Ebb and Bill should submit an article to Good Old Boat on this project.

[Mike Goodwin]

Make a template of the hole but 1/2" more radius , use a 1/2" bushing with a spiral upcut bit on a router , clamp the template in place , run the router around the template and you have a perfect hole with no snatched drills trying to break your arm .
It is safer , faster and cleaner than using hole saws .
The router bits are dirt cheap .
I have done huge holes with this method.
HDF board makes the best template material BTW .

[ebb]

OR:
make the template (how do you make the template, tho? AHH-HA let's use a holesaw!) of the exact size hole you need.
Then use a router bit that has a roller bearing right on top of the bit that is the exact width of the bit. Most common are 1/2".
Attach the template, plunge in the router and bit and merrily around you go.
Throwing glass fiber dust everywhere. Can always tape a plastic bag over the area inside to catch most of it.

This is a very clean hole method for sure. You need to figure how much blade depth you need so that you are always running the bearing of the bit around on the template. Imco the easiest templates to make are with tempered hardboard. And you could use an adjustable circle cutter in a drill press to cut any size custom hole for a template. But since hardboard is usually 1/4" you won't be able to raise or lower the bit any.

Al's method is the quickest, simplest and most problematic.
ebb's method continually guides the holesaw cutter in without the centering drill bit to foul things up.
The router method is most elegant, but requires most equipment.

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Was thinking about this again:

From the standpoint of the weekender and someone who doesn't have access to a shop - and an event like this is propably a one shot deal - Al's method is the easiest.

So you have this scrap with the pilot hole already drilled. Instead of clamping it on the inside, clamp it on the outside like Bill shows. The 1/4" hole would be easy to center in the old hole with light coming thru it. In fact, as Bill shows, you can take the scrap and place it tight against the companionway trim, goes a long way to keep it unmovable.

Even better, what you could do is place the scrap where it will clamp most securely (as Bill has shown) and with a flash light and a pencil trace the hole you want to enlarge on the scrap from the inside.
Unclamp it, find the center, then drill the pilot hole with a normal bit, clamp it back in place, and holesaw away using the drillbit hole for the pilot bit.
When you cut the disk out of the scrap, stop and remove it from the holesaw.
Then proceed to cut the fiberglass using the hole in the scrap as the guide. You can make minor adjustments of your template befor you cut.

When a pilot bit sticks out any further than 1/8" from the rim of a holesaw it can lead to binding.
So that if you are working from the cockpit and set the bit say 3/4" out to reach the scrap clamped on the inside of the cabin and liner yer asking for trouble.
The inside/out method above might work better. Hole saws work much better without the pilot bit. In fact you can rock the saw (VERY SLIGHTLY at slow speed) in its guide when you get to holesawing the hard stuff without the center bit, especially if you bought a cheapy special for the one job.