Ms. MAK 20SF

[Blue_Heron]

Originally Posted by slowJEEP

...Any thoughts on a 600-3000 rpm polisher w/ abrasive disk for grinding fiberglass vs a regular ol' dewalt 7" grinder?

I have a couple of these:

http://www.homedepot.com/p/RIDGID-15...ct_description

Fiberglass is fatal to electric tools, eventually. I had a cheap sander polisher that died pretty quickly. The Rigid 7" grinder at 8000 rpm works circles around the sander polisher, especially if you use the flapper disks Normagain suggested. The quality of Rigid's power tools is on par with Porter Cable, Bosch, Makita, or DeWalt.

There are two things I like about the Rigid product over the competition. One, the trigger handle rotates 90° right or left. That makes it very comfortable to use if you are using a cutoff blade or grinding at odd angles.

The second thing is the lifetime guarantee. Technically, you have to register your purchase for the guarantee to take effect, but there may be a little wiggle room on that. Home depot replaced one that I hadn't registered. It was several years old, and I had misplaced my receipt. I'm sold on them.

Dave

[slowJEEP]

That Rigid Grinder is genius. Thanks all for the suggestions.

Onto another matter. It's time to order material and I'm wanting to go with Coosa BW26 for the transom with epoxy.

I'd say the stuff that came out of the transom was 1.5"s thick and it'd be safe to replace it with the same thickness. However, since I'm going to run a full width dive platform/engine bracket, I was thinking about going with 1" coosa. I'm fielding opinions so please comment.

I know the 1/12*b*h^3 means it will be roughly a 3.375x decrease in stiffness/strength from 1.5" to 1" but I expect the bracket will more than make up for it.

My desire to skimp on material is the proportional decrease in weight and $. I figured I was bias and could be set straight by the CSCers.

[FAS]

I would go by experience,not numbers,1" foam for a transom is not enough if want to feel confident that you did the right thing. I am sure it would work, but...

[FLexpat]

Not sure about the 20 but on my 23 it was 2 layers of 5/8" stapled together. Something to think about; You are adding a pretty good sized lever arm with that platform and you really don't want the transom flexing but you are right to be thinking about weight. The volume of the 1.5" transom in my 23 is 3 ft3; 78 lbs of Coosa 26 and 100-120 lbs if plywood. A 1" Coosa 26 core would weigh 50 lbs for a savings of 26 lbs. over the 1.5" coosa. Not a lot of weight savings, maybe a little in $.

[martin]

Originally Posted by slowJEEP

That Rigid Grinder is genius. Thanks all for the suggestions.

Onto another matter. It's time to order material and I'm wanting to go with Coosa BW26 for the transom with epoxy.

I'd say the stuff that came out of the transom was 1.5"s thick and it'd be safe to replace it with the same thickness. However, since I'm going to run a full width dive platform/engine bracket, I was thinking about going with 1" coosa. I'm fielding opinions so please comment.

I know the 1/12*b*h^3 means it will be roughly a 3.375x decrease in stiffness/strength from 1.5" to 1" but I expect the bracket will more than make up for it.

My desire to skimp on material is the proportional decrease in weight and $. I figured I was bias and could be set straight by the CSCers.

I would not go with a 1" transom core.. Not enough meat there when you pull in your bolts. Especially when hanging a bracket. Once you crush the foam just a little it shears off the glass then turns to snot.. Adding a bracket will just compound the force applied to the top bolts and bottom bolts..trailering with a motor dangling off there will really cause some flexing. Water gives a little ..concrete potholes don't .. 1" is great for a 20 hp ...clamped to the transom.. Hell my 13 Boston whaler has a 1.25" transom with a 50 hp and it has cracked some...just my 2 cents

[flyingfrizzle]

coosa blue water 26 is a great product for transoms, it has better compressive strength than most other foams but I would go with two 3/4" pieces bonded together or just one 1 1/2 piece. I would think one single 1" piece will be thin unless you built it up real thick on both sides with cloth biax but then to would be way to heavy.

[FishStretcher]

Originally Posted by flyingfrizzle

coosa blue water 26 is a great product for transoms, it has better compressive strength than most other foams but I would go with two 3/4" pieces bonded together or just one 1 1/2 piece. I would think one single 1" piece will be thin unless you built it up real thick on both sides with cloth biax but then to would be way to heavy.

I thought about this a little. I would agree that 1-1/2" foam is better. But the specific gravity of fiberglass in resin at 40% glass content is something like 1.5. And decent plywood about half that. 0.7 If Coosa is 26 lb/cubic foot, that's a specific gravity of ~0.4.

So if the old plywood weighed 50 lb, replacing it with glass would be a bit over 100 lb. But an additional 1/2" of glass would be about 35 lb. Plus the inch of foam another 17ish lb. For about 50 lb again.

So I think the weight would wash out versus *dry* plywood. But you would have another 1/2 of glass in the transom. And a foam core. Not as light as 1-1/2" of foam, but not a terrible tradeoff.

Check my math, though. I am running out the door to work.

[slowJEEP]

Duly noted. Thanks for the input.

[Blue_Heron]

Originally Posted by flyingfrizzle

coosa blue water 26 is a great product for transoms, it has better compressive strength than most other foams but I would go with two 3/4" pieces bonded together or just one 1 1/2 piece. I would think one single 1" piece will be thin unless you built it up real thick on both sides with cloth biax but then to would be way to heavy.

X 2.

Only thing I would add is the inner laminate should be 3/16" thick to maximize bending stiffness and to prevent core crushing due to bolt loads.
Dave

[slowJEEP]

Started grinding the old wood and blistered glass off the transom today. New grinder and flap disk made quick work for a little while. Half done and the flap disk is slower. Anyone have a better glass grinder than a flap disk?