Ms. MAK 20SF

[FishStretcher]

I agree on the fatal to tools bit. At least those with brushed motors. I buy the cheapest electric sanders I can. The flapper discs are amazing. Until you hit something other than polyester resin.

Polyester resin is brittle, epoxy and vinylester are tough. Personally, I save the $$$ on the tool and buy more flap wheels with the coarsest grit I can find. 24 grit if I can get it.

Although a rotable handle and trigger assembly sounds nice.

Originally Posted by Blue_Heron

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

[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?

[slowJEEP]

Some photos as of late:

Pre filter for the shop vac. I guess I thought the can would hold up to the partial vacuum a little better.


I put a scrap piece of expanded metal in there to help hold it's shape. It worked a little better.


Got the transom ground down some. Gonna take a few tries to get my grinding muscles up to speed. I was surprised to see how poorly the mat bonded to the roving on the transom. You can see I've ground a lot of mat away and aim to keep going.


Looks like they used coremat in the layup of the hull sides. Is this common?

[Blue_Heron]

Originally Posted by slowJEEP

...Looks like they used coremat in the layup of the hull sides. Is this common?

I don't think Coremat was available when these hulls were made. Could it be from a previous repair?
Dave

[slowJEEP]

I think it goes all the way around. The hull is an '88. I don't know that it's coremat by name, just looks similar.