I need to stiffen the transom of my small aluminum

Hi all and greetings from Rhode Island.

I have a 11' Aluminum I bought last summer I outfitted with forward controls and a vintage Evinrude 18hp outboard. I have since bought an older 25hp outboard and need to stiffen the transom for obvious reasons. The 18 too much motor for this thing but I got a deal on the 25 I couldn't pass up. This is just a fun little boat for me and I can't wait to have it all ready for next season.

I broke the transom gussets last year when I was jumping some waves having some fun. I don't plan on doing this ever again but I want to stiffen the snot out of the transom. I have some 5/8" oak bolted to the transom but that doesn't cut it.

I assume making new gussets would be the first thing, but what else do you think I can do to stiffen things? Where do I buy thick aluminum? I have a 225a AC Lincoln Buzzbox I can use if they make rods for this!

Thank you everyone. :lol:

Also, I have no idea what brand boat it is or what year it is, but it looks pretty old

Pictures attached.

edit: I'm sorry the pictures went in upside down. They're the correct orientation on my desktop.

Hey there Pete - I think the 25 hp is going to be unsafe on your 11 footer. If you need to reinforce the hull, make it so the extra stiffness tapers out toward the bow. If you change rigidity suddenly, it will fatigue at that point.

Welcome aboard Pete !!

if you ask 10 people about transoms - you will get 15 good solid answers.

in my world, I would remove everything on the inside of the metal.
make a cardboard template of where you want the new wood.
laminate two sheets of 3/4" exterior grade plywood together.
cut the desired shape out with your power tools.
preserve and paint accordingly.
fabricate 3 new knee braces that will withstand the rigors of the larger motor.
thoroughly inspect all seams and rivets in the transom area for stress cracks.
if you "broke the transom gussets last year" - then there is undoubtedly fatigue
and stress within the transom metal that you can not see with the naked eye.

simple as that


oh, and I totally agree with Scooter: 25 hp is going to be unsafe on your 11 footer
your boat = your call

and, your statement of - - - "I assume making new gussets would be the first thing,
but what else do you think I can do to stiffen things? Where do I buy thick aluminum?
I have a 225a AC Lincoln Buzzbox I can use if they make rods for this!"
tells us that you have no clue as to what you are doing - or about boating in general.







.

Johnny said:

View attachment 1


Welcome aboard Pete !!

if you ask 10 people about transoms - you will get 15 good solid answers.

in my world, I would remove everything on the inside of the metal.
make a cardboard template of where you want the new wood.
laminate two sheets of 3/4" exterior grade plywood together.
cut the desired shape out with your power tools.
preserve and paint accordingly.
fabricate 3 new knee braces that will withstand the rigors of the larger motor.
thoroughly inspect all seams and rivets in the transom area for stress cracks

simple as that


oh, and I totally agree with Scooter: 25 hp is going to be unsafe on your 11 footer
your boat = your call

and, your statement of - - - "I assume making new gussets would be the first thing,
but what else do you think I can do to stiffen things? Where do I buy thick aluminum?
I have a 225a AC Lincoln Buzzbox I can use if they make rods for this!"
tells us that you have no clue as to what you are doing - or about boating in general.







.

Click to expand...

Thank you for turning around the pictures.

Been boating for many years! Started with an '86 Chris Craft 17'. Three engines later, 75-90-115 I still have it. Never had an Aluminum before. I like the vintage look of the boat and the '52 SeaHorse I just bought. Never modified a boat but many an engine in my time.

I meant "where do I buy thick aluminum" meaning - if I were to make a template of the transom and perhaps buy a plate of aluminum to have welded to it. I am by no means a professional, but I get stuff done. I have people I teach HS auto mechanics and we have a welding program as well at my disposal if mine won't do it.

I would opt for something along this nature.
6 braces fabricated as per example, welded at the cuts.
I would marry two together opposing each other to make one very rigid brace. (three sets).
remove the end caps and install 1/4" x 3" flat bar from the transom down each side about 5 feet
with the end bent over and bolted to the transom like Scooter described.
of course, cut off the excess of the bolts.


you have all winter to figure it out - - - - -




.

That's a great idea, Johnny. Is that your boat?

Thank you for this.

no, not my boat - a member here did a thread on his mod a few years back.
https://www.tinboats.net/forum/viewtopic.php?f=3&t=18553

use the "search" button - "transom"...... many good reads there.
and on the topic of "search" check your phone book yellow pages (or Google)
for METALS or METAL SUPPLY in your area. also, check your local
recycle company and see if they sell aluminum to the public.
and if that doesn't pan out for you, there are several online metal
suppliers that ship their products...... if you only need small amounts,
try the Big Box Stores. Farm Supply and Tractor Supply in my area are good.

this is my boat - '59 14ft Crestliner. The other one is a '59 14ft Lone Star.
both are in the process of being stripped and repainted with new wood furniture.
my transom board is two sheets of 3/4" thick lateral stranded fiberglass panels
with a 1/2" support board on the outside of the transom that has 1/8" aluminum
plate bonded to it for the motor mount.
the 25 Johnson is sold and I have a new 1958 Johnson Super Sea Horse 35hp to go on it.
They are not fishing boats. They are strictly pleasure runabouts for cruising the waterways.