building outboard bracket?

I am trying to plan an outboard bracket, I hope to build it out of 3/4 ply and glass..the outboard is a 50hp and weighs 260lbs..any ideas? can it be safely bolted to the transom? should it be glassed on the outside and bolted on the inside with aluminum angle stock? any ideas would be appreciated..thanks..Mick

 

My biggest problem is that I always tend to overbuild things like this by a longshot. What configuration are you thinking of using?
. __ . _ ._ . __
|__| |_|_| /__\

Are you planning to double up the ¾”? Or maybe add a center member or angle the outside members (or maybe that would be a pain, but it might look very elegant. Of course then it would be more difficult to find the right interior angles, esp. from aluminum). I wonder if you would want to add a few small 2-3” horizontal or vertical stiffening strips before fiberglassing to make it really rigid – probably not necessary, and maybe a moisture trap, but a thought.

I like the idea of using aluminum angle brackets. My only concern might be for the coating/finishing where the angle brackets are (I would have a hard time not glassing the inside too for moisture, at least with a thin layer, but of course, it’s a pain to glass an inside corner without a radius. I would be concerned that just epoxy alone might crack away from the aluminum and leave wood exposed to moisture.)

Bolting to the transom shouldn’t be any problem at all.

One advantage of a pre-made steel outboard bracket which you will be missing is the ability to adjust the outboard's up-down position to get the best performance. Even if you didn’t get a hydraulic bracket ($$$), there are many which have a vertical screw so you can make minor adjustments to the outboard’s height.

 

outboard bracket

I also tend to overbuild these things, I would like to incorporate a full width swim platform with the supports for the outboard mount angling outboard somewhat, I can glass the inside also, maybe add 45 degree cleats to screw the ply into and glass across, what is the preferred method? adding a swim platform allows bolting across the whole transom with proper back-up blocks on the inside...the premade aluminum brackets are really nice but $$$$..thanks for the reply,,Mick

 

So what kind of boat is this for?

Do you need a bracket because the boat doesn't have an outboard well, or did you decide to build the bracket to get better performance (for vertical adjustment or to get the horizontal setback) or is it to get a nicer swim platform than the typical little platforms beside the outboard?

Should be a fun project

 

old sportcraft

I am starting with a 78 24 ft sportcraft, I have gutted the entire thing and will replace the stringer grid, deck and transom ply, I have a new yamaha high thrust 50hp 4 stroke...I want a slow, economical trawler type of thing, my wife and I are going to cruise, I figure cruise speed in the 8-9 knot range at 6-9mpg...interesting concept? most boat types say "yo man, it will never plane with a fifty"...they are correct..it will hopefully be a quiet, cheap to run cruiser, I am building a 3/4 cabin with dinette, galley etc...great for two...still trailerable...I stopped at a local boat shop and checked out a fiberglass outboard bracket with twin johnson 200's..nice..I got some ideas..that bracket wasn't built near as sturdy as I plan this one...hopefully 100% complete by spring...in water and running sans cabin by the end of aug this year...thanks for the replies...Mick

 

I think that a 78 sportcraft is a pretty "hard lined" boat, and that's probably good for the aesthetics and ease of building the bracket. I was starting to think that you might want to build in some curves/radiused corners if you were doing a fiberglass bracket for a newer heavily-molded boat, and that would make the project much more time consuming. But I think it will look just fine to do a hard-edged wood/fiberglass bracket because it will match your boat nicely.

Also, since your objectives are probably #1 to free up cockpit space and #2 to have a more seaworthy boat minus the big well in the transom rather than performance/adjustment capability, a homemade bracket stacks up much better against a factory bracket.

I was looking at building a bracket myself a couple years ago because I needed to add a couple inches of height to the outboard for both performance and to reduce the draft. First I thought about wood/fiberglass, but I wanted mine to be a bit more compact because it was for a small boat. I then considered having a steel bracket fabricated (because I never learned to weld) but somehow I stumbled upon an aluminum one-piece cast bracket which just fit my needs for ~$100 (max for a 35 hp engine, and I had a 35 hp. 2-stroke). In hindsight, wish I had built one from scratch...

I will want to hear or see some pictures of how your project turns out

P.S. I am surprised that a 50hp. four stroke weighs 260 lbs. I thought they were a little lighter than that...

 

Types of wood

I'm concerned about the FRP acting as a moisture trap, and the wood rotting. If you would like to avoid wood there are some dense foams - essencially blocks of plastic - available now as cores for transoms. But the right wood can be good without FRP. I would recommend Afromosia or Iroko (African Teak) or Black Locust. These are rot resistant hardwoods that glue well (unlike teak & oak).

Laminating wood or using a high quality plywood (perhaps made of one of the "Africam Mahoganies" - see WoodenBoat Magazine for suppliers) also has benefits - better dimensional stability and less chance of splitting.

I am for saturation with epoxy, ESPECIALLY AT THE END GRAIN! Many people don't understand that most of the moisture absobed by wood is absorbed at the end grain. That, after all, is how trees get water from their roots to their leaves. If you can let the wood air dry for a few months, and then seal the end grain with epoxy, you will have a great structural material. I recommend painting it with an epoxy paint compatible with the epoxy saturation.

 

thanks

thanks for the helpful replies, to control the rot I may not completely enclose the box, the boat will be kept on a trailer when not in use..3/4 marine ply should suffice???I will heavily reinforce it with roving and west, correct! the sportcraft is boxy and the transom has a very slight radius, I will encorporate a full width swim platform, convient and adds strength...I surely intend to saturate all the ply with west to keep the h2o out...thanks again..i'll keep you posted...Mick

 

epoxy saturation

My point is that the edges need the epoxy more than the faces do, so use multiple coats on the edges, and good luck!

 

Hey Mickster,

For an area subjected to soooo... much stress, you should use Biaxial Tape or fabric. It is much more structural than roving or standard cloth. Epoxy coat every sqaure inch of plywood, then build up a 1/2" radius on the inside corners(with thickened epoxy), cover all joints and areas accepting bolts with a couple of layers of epoxy wetted biaxial tape. Epoxy saturate any bolt holes before bolting, sand paint... You can probably find the biaxial tape on http://www.boatbuildercentral.com/. You also may get some good engineering advice on http://www.amateurboatbuilding.com/. A second opinion can never hurt. I have not yet felt the need to build a bracket, and have no affiliation to eihter of these sites.

 

Bracket? This one will carry a merc 300x (515lbs+) its cast out of 1/2" aluminum.

www.freewebs.com/mytuffboat

 

owner of a 20" chris craft "sea skiff" (central consolle), 150 hp, i'd like to buy a bracket (it may be possible an Armstrong one).
any support for my idea ?
do anyone had the same experience with a similar boat ?
many thanks

 

I haven't installed a bracket, but have some info on it.

Installation Tutorial
http://www.diy-boat.com/Pages/Archives/links/prig982.html

Bracket Manufacturers
http://www.armstrongnautical.com/Brackets.htm
http://www.stainlessmarine.com/home.html
http://www.gilmarine.com/products/gbracket/brackets.html
http://www.hermco.net/seamark_bracket.htm
http://www.seamount-mattson.com/
http://www.dadmarine.com/index00.htm