Transom reinforcing 34 Silverton for outboard conversion

knees

The PIRATE House comment was a refferel to what locals call the PILOT House restraunt and tiki bar oceanside at mm100.

BTW, you won't be using any "cloth". As mentioned mat is what will be appropriate for between layers. As for the "knees" you will want to make them out of plywood laminated to at least 1.5" + and to be as big as possible, to at least go as high on the transom as the top bracket bolts and preferably be at least an equalateral if not reaching as far forward on the stringers as possible. I would also bolt them to the stringers as well as adhere and glass.

Steve

 

OH, de pirate house, yep, they rebuilt the place recently... don't make it all the way up there much...all of 2 miles away...hard to get back on my Schwinn when it gets late....

 

I'm gonna get some 12mm Okume plywood, put three layers with glass mat and plenty of (epoxy or vinylester resin between layers, cant them 10 degrees, stagger the joints (10 ft beam at the transom), screw them together every foot oc. The transom is about 60 inches hi at the center, deadrise of ? so about 50 inches hi at the sides.

The top 20" of the transom inaccessible without removing the entire cockpit (single piece 10' x 10' glass/resin structure). If I build up the bottom of the transom only, the bracket (with 2 x 300hp engines) will bolt up to the reinforced transom. I may end up cutting a door in the top part of the transom for easier access to the swim platform.

After doing all of this work, I want to insure the boat. I'm guessing that the insurance company will want some proof that this design was ok. Any suggestions on how to find someone qualified to look at the design, give me some sort of ok?

 

I finally finished reinforcing the transom with 6 layers of 3/8" okume marine plywood with 1.5 oz glass mat between, and a final layer of biaxial. Turned out to be just over 3" thick when I drilled thru for the bracket. I haven't put the braces in yet, figured I should bolt the bracket on first so I don't block any bolt holes.

This turned out to be more work than expected - like most of my projects. If I had to do it over I'd weld up a steel framework for the reinforcing. Getting 10 ft. wide pieces of plywood in there was a problem - I had to cut each layer in half to fit them in place in the bilge. I could have used them full size if I'd have taken the cockpit floor out - but this would mean taking the whole damn boat apart.

The other part that made it difficult was that I screwed each layer down with about 100 screws per layer, cause the transom is curved 24 ft. radius. This didn't look like it was much curve, but when I started screwing it down, in order to get the ply to follow the transom, I needed screws about every 6 inches. That made about 300 screws going thru the glass transom - that I had to cut off, divot out and patch.

Now I'm working on mating a used 4 engine Stainless Marine bracket made for a flat transom boat to my curved transom.

 

outboard pods

Im hoping to put two outboards on my 28 Zeta and I found your post. Im worried my boat may be too big heavy for this as most pods seem to be for smaller boats. Yours is the first ive heard of it being done on a larger boat.

How did the conversion go? advice?

 

You best check the last active date for the poster(s) you hope to hear from, to ascertain whether they are still around. I know nothing about your boat, but 28' is well within the length of boat that outboards are successful on, your hull shape may determine what will work on yours.

 

R u Happy with your conversion to outboards?

Thanks for the response. Are you content with converting to outboards? Did you experience and of the problems that can happen, transom not strong enough, boat porpoises, trim problems etc.?

 

Sorry for not posting my results on this project here. I did finish the boat - 1978 34' Silverton Sedan - flybridge cruiser with 12.5 ft. beam. I mounted an aluminum bracket - I think the bracket extends out 30 or 36" - I mounted it 18" above the water line, hung two Mercury Optimax 225 hp outboards on it - 6 ft. apart. The boat is a totally new boat - tops out at 30 knots, cruises at 22 knots while using 1.4 nm/gal fuel burn. That's compared to about 16 kts cruise at .75 nm/gal with the stock 260 hp inboard Crusaders the boat came with. Totally new boat - can run at 16 knots on plane in rough water - rides deep in the water which smooths things out, but if it's not too rough - under 2' seas, it is easy to get up out of the water and really fly, comparatively. I do 22 knots at about 4000 rpm. I have three blade SS props - I think 17" pitch.

The whole project on this boat was very time consuming. I wouldn't do it again!!! But this boat is rock solid - I even cut a door way in the transom so we can step from the cockpit right out onto the platform. Of course the engines take up most of the platform, but it is easy to get to the dive ladder with scuba gear on.

 

Congratulations!

Thanks for responding! Everyone I talk to says my boat is too big, it wasnt designed for it, rear end will be heavy, your boat will porpoise, etc. etc. Yet many owners of these converted boats seem happy with them?? On THT, several Bertram 28s were converted to outboards despite the doom and gloom advice they were given and the owners seem to have no problems.

What does your boat weigh fully loaded? My boat weighs 10, 0000 lbs and i suspect if you can get yours to perform like that with 225 optimax's, I might be able to perform similarly with 175 HP optimax's?

Did you choose the optimax rather than the four strokes cuz lighter? More powerful? Did you buy them new?

Are you going to post any pictures? Love to see it.