Bracket theory

[thehermit]

Originally Posted by strick

What makes you think that adding foam to the interior of the bracket will give you more flotation? All it does is add more weight to the bracket. If your bracket is water tight then there is no need for foam!

strick

Dito! No Foam...small amounts of water does find its way on mine. Would hate to have foam in there soaking it up.

[FishStretcher]

Originally Posted by thehermit

Dito! No Foam...small amounts of water does find its way on mine. Would hate to have foam in there soaking it up.

Yep, the foam is 20lb. I just worry what happens with a leak. Then you have an additional 100lb on the transom, and the outboard 30" back. That thought is scary out on Buzzards Bay

I don't want to foam it. I might foam it inside polyethylene bags, so I can remove it if it doesn't leak.

[Bushwacker]

Originally Posted by FishStretcher

From what I can tell, all the (flotation) brackets all have centrally mounted flotation volumes. And no flotation out at the edges.

It seems like at rest, some flotation under the wide swim platform would help lift the outboard out of the water even more. Why isn't this done? Is the issue making the boat roll in a sea that was coming at an angle to the stern?

Or is there some other reason, like practical construction issues, or something else?

Fish, you might want to send a PM to Don Herman with some of your questions. As I mentioned in a previous post, the only reason Bill Potter did NOT make the tank wider on the Hermco bracket is to leave room under the swim platform for a ladder. Don is now looking at a wider-tank option because so many folks are going to the heavy 4 stroke motors. I think he was just going to extend the existing bottom surface and side of the tank all the way out to the second step. I don't think there is any need to follow the contour of the bottom on your bracket; if you eliminated that step, it would give you even more flotation!

I asked Carl Moesly one time what he thought about brackets, and he said "Why not just make the boat longer?!" That's an interesting concept . . . make the bracket bottom just an extension of the boat bottom, put the trim tabs on the back of the bracket and gain the advantages of a longer waterline length and planing surface! Sort of a "Euro transom addition" rather than a bracket!

As far as foam in the bracket is concerned, ANY water leaks are unacceptable, just like in the boat itself, so focus on building it right and eliminating any potential leaks!

I'll get you some height dimensions off my bracket and send them to you later today. Denny

[kneedeep]

take a look at the built in bracket on the 27' silverhawk boat.

[bly]

Originally Posted by kneedeep

take a look at the built in bracket on the 27' silverhawk boat.

sea craft stretched original hull to 25 and then a 30 inch fiberglass bracket? This will only confuse the original question of an aluminum bracket for a 20 ft sea craft that he wants to widen, Bob Seidlemann did not work with a 20 sea craft when he was alive. It was a 23 ft when sea craft company was closed up before 1995. His main claim to fame on this as he invited me there to explain while doing it was raise the original floor. and nicer and new hatch openings.The original poster is wanting to widen a single aluminum bracket for more floatation to the second lifting strake instead of the first. I believe there will be almost No floatation effect because of how little water it will be in. I have my own fiberglass mold I made from one of those seidlemann brackets for a twin engine sea craft hull shape. I am doing a 20 ft sea craft now and will have to make my bracket smaller because it is way to big. He also wants to fill the aluminum bracket with 2 lb floatation foam? I can not tell you how much and how heavy that so called closed cell foam is and how many boats I have had to remove it from. To the Original Poster If you are that worried. And I was very worried on my fist bracket that I made for my personal 23 ft formula. I would in your situation install a high water alarm in the bracket. Now at the lowest point of the bracket but above the internal flange drill and mount a 1 in diameter cheap nylon through hull with a ball valve. leave it open and run the wire through it to the float switch for the high water alarm. If you ever needed to close the valve rip the wires through and close the valve. If you do get some water in the bracket it will drain into the bilge and be pumped out by your normal bilge pump. Do not fill a bolted on aluminum or fiberglass bracket with floatation foam. Very bad Idea. Becareful about putting to much bracket on a small boat. It may be too much

[FishStretcher]

So I can't do some of the mods to the 30" bracket I wanted with a Bridgeport- it won't fit. So I decided to look at making it into a 24" bracket with a plasma cutter and TIG torch. I modeled it up and it looks like about 430 lb flotation, less 105 for the bracket mass if I include the side tanks.

Below are illustrations of the bracket placement with a 20" Yamaha F100 motor. It might be a little low?

[thehermit]

are you planning for trim tabs?

[FishStretcher]

Originally Posted by thehermit

are you planning for trim tabs?

Not planning for them, no. There is ~8.25 inches outside of each flotation box to the edge of the swim platform. So if I had to, I might be able to squeeze some in.

My strategy is that with a rather tall fuel tank in the fore part of the center console with the batteries in the center console, and the fact that I sawed off the console seat and will use a ~100 quart cooler there for a seat- that will pull the CG forward enough to keep from porpoising.

All of this is done, except for the seat/ cooler- that is in progress. There is no under floor fuel tank now, just ~50 gallons of removable foam insert.

All this might not be enough, but I think the CG was a bit forward of optimal this year, even with the kicker (but no bracket). It was very easy to push the bow down forcefully into the water on plane with just motor trim. So my hope is that fore- aft CG will be not require trim tabs. There were a few times I wanted them this year to correct roll.

[Wildman]

Originally Posted by thehermit

are you planning for trim tabs?

If you arn't, you should be! Leave room for a set of Volvo QL tabs.

I would not shorten that bracket any, here is a picture of the clearance between my transom and 225 oceanpro, tilted all the way up. Its mounted on the lowest hole right tight to the top of the bracket. I may have an issue if I have to bump it up a hole, I dont want to think about what would happen if the bracket was 3in shorter!

[FishStretcher]

I will think about tabs, but I can't justify a 30" bracket on a 20' boat with a 100hp outboard. I modeled up the Yamaha and it has 2-3" clearance when it is tilted fully up. The extra 6" of length on the bracket is just working against me when I am on plane, so I think I will chop it to 24"