Inboard Issues

[Mike Goodwin]

Sizing a prop isn't that hard to do . If it isn't turning up the rpm's then it is too big or too much pitch or both . It is probably too much pitch .
In a perfect world a 12" prop pitch would try to advance the boat one foot per shaft rpm ( not engine ) .
So if you are trying to hit 6 knots ( 36480' per hour ) with a 12" prop , you need to make 608 shaft rpm's ( with no slip ) .

I had that motor, I think, 10hp Yanmar and it would not swing a 9x9 prop .

[mbd]

So if you are trying to hit 6 knots ( 36480' per hour ) with a 12" prop , you need to make 608 shaft rpm's ( with no slip ) .

Mike, just curious - did you know those figures off the top of your head?

You're talking to a guy who can't even get the gd prop off! Having had a new shaft installed this summer, I figured it would be a simple thing. But I tried this weekend, and tried again, and tried some more... I removed the nuts on the shaft, then tried hitting it with a rubber mallet, rotating, whacking it, rotating, whacking it.. I tired putting a block of wood against the prop by the shaft and whacking that, ad nauseam. I ended by spraying the thing down with WD40. I hope that's not bad.

Got any tricks? A quick web search tells me I could use a "prop puller", whatever that is.

I'm trying to remove it so I can take it a boatyard and have it looked at.

[Mike Goodwin]

You need a prop puller , looks like a gear puller .
You can make your own if you cant find one to borrow.
2 pieces of 1/2" all thread rod about a foot long , 4 nuts and washers .
2 pieces of heavy metal , one with a U shaped hole cut out of the side and holes drilled for the all thread near the ends .
I draw it for you after dinner .
The size and pitch of the prop are embossd on the hub , something like 9x9 or 8x7 , look for it .

Figures aren't on top of my head , nothing is anymore , but the math is simple enough and I'm good at simple math and I know a knot is 6080' , but where are my car keys?

[Mike Goodwin]

OK, quickie sketch .

Put all thread through small holes , notch goes behind prop and plate with no notch goes against end of shaft. Tighten evenly on nuts until you have a good strain then whack it with a wood/leather or rubber mallet ,tighten some more and whack , repeat till it comes off .

any ?

Whack the puller , not the prop !

[mbd]

Mike, many thanks! I get the concept methinks. And it looks like I may be able to borrow a real prop puller...

[Mike Goodwin]

I finally found the coupler.
It is a Vetus Uniflex model 1225 for a 25mm ( 1") shaft .
Allows 2 degrees of mis-alignment .

Sells for $431 , I'll take $ 250 . In the box with instructions .

with a 4" connection for Hurth, Velvet, TD, ZF, PRM and other transmission makes.

If you need an adapter flange, they are listed here and run $110 - $149 ;

http://www.vetus.com/flex_couplings/flex_couplings.cfm