How thick transom do I need?

[zymox]

Hello everybody

I'm new to this forum, boating and also from Sweden so you have to excuse me for not using the right terminoligy and for my bad English.

Background: I bought a French fiberglass boat named Juet Ritz from 1966. It's approx. 6 meter in length, about 2 meters wide and classified for 150 hp. As you all can imagine the transom and all other wood on this fiberglass boat was soaking wet and all rotten so I decided to restore it.
Yesterday it was time to check the transom and as I suspected it was all gone, smells and looks like a bag of flower planting dirt when I did the drilling-test.

However, I have separated the over-hull from the bottom-hull and measured the transom thickness. It only measures about 16mm of thickness across with an reinforcement plate of 10 mm in the midsection so a total of 26mm (approx.1 inch) where the engine is mounted. Add another 2*2 mm for the fiberglass and you have the overall thickness of my 150hp classified transom :redface:

My motor that I have on the way home for this boat is an Evinrude looper 140hp from 88 with a weight of approx. 160kg and even though I'm not an Einstein I can understand that the above is not going to withstand all that weight and power for a very long time.

So, my real question is: How thick do you recommend me to make my new transom to withstand the weight and the power of my looper?



Tanks in adv. and sorry for my bad English.
BRGDS

 

[oops!]

Re: How thick transom do I need?

your English is far better than you think my friend.

welcome to iboats !

if i remember correctly.....the thickness of an out board transom is just under 2 inches....(im a canadian, and use the metric system for everything except small measurements...lol)

if you go 1 and 3/4 you should be good....

the thickness of the transom is determined by the maximum spread of the hooks on your motor. so if you measure that, you will know how thick to make your new transom.

the horse power rating is determined by the length and width of your boat.

one thing.....just make sure it is well tabbed to the hull, by adding fiberglass to the edges of the transom that extend on to the hull. this, in conjunction with raised sections of the stringers called "knees" where the stringer meets the transom, will make your new transom very solid.

cheers
oops

 

[zymox]

Re: How thick transom do I need?

Thank you for your answer.

Then I will do one cording to your recommendations. 1 and 3/4 Inches should be something like 44.45 mm.

BRGDS
Zymox

 

[BillP]

Re: How thick transom do I need?

Two layers of 19mm (.75) ply plus the glass laminations would give what you are looking for...it's good for twin 140s.

bp

 

[zymox]

Re: How thick transom do I need?

Hello my friends

I have done the transom "rip off" and got another question for you pro's out there.

Do I loose something in changing the shape of the inner layer or should I stick with the original?

(I'm starting to think I may fool my self a bit since I believe the shape of the inner-layer together with the laminate will actually be stronger then just a plane sheet. I think of it as a sheet of metal, it's very easy to bend a metal sheet over the sheet-side but almost impossible to bend it if you tries to bend it over height-edge... I don't know how to explain what I mean but I think you get what I'm thinking)

If you look at the pictures you can see that it was an all over transom sheet as the outer layer and a 3 piece inner layer in the midsection raising approx 10mm. My plan was to make it in 2 pieces.

I will have to make it in 2*18mm plywood also since the 19mm is not a standard here in Sweden. It's possible to order it but it will take something like forever to receive it.