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Finally closing up both in/out through hulls from the old head and removing the plumbing in the B20, and the hull here is only 1/4" thick.
I understand the 12-1 guideline but how do you you safely compensate for a larger hole in a thinner area of the hull...

Using the 12-1 it would be a 1 1/2" diameter grind from inside and out..

The holes are 1 5/8" and 1" ... obviously it won't work here, I was thinking of 24-1 so 3" grind area..

How much overlap is safely required on holes ..???

BTW after 42 years the wood backing blocks were solid and bone dry...

Ray

12:1 doesn't refer to hole diameter, but thickness of the hull...

If your hull is 3/8" thick then a single side scarf would halo the hole out to 24/8" or 3". On a two sided kerf, (what I prefer), divide the hull thickness by 2 = 3/16". Scarf both sides of the hull at 12:1 = 24/16" or 1 1/2" out from the hole. either way, the perimeter of the hole is reduced in thickness to zero.

The hole size could be 1/2" or 10", the scarf would still be the same halo around the hole and only dependant on hull thickness...

12-1 "out from the hole" ..those were the four words I was missing ..
Sometimes the stupidity sticks with me all day long...

Thanks Capt Pat..
Ray

Ooppps, got my math wrong...

12 x 3/8 = 36/8 = 4 1/4" for single / 2 = 2 1/8 for double

Capt Pat, No Problem .. I think I'm good..The hull measures 1/4" so a grind from both sides will be 1 1/2" from outer edge of hole ..

Correct???

You got it...

Thanks Again..