Transom reinforcement

[baiwan]

I ran my boat with a Suzuki DT 65 and it was OK Now I want to run it with a 90 hp motor which is 55 lb heavier and 25 hp stronger.
I have a 15 foot 22 year old boat that is in best condition and wonder if I have to reinforce the transom for the more powerful motor, or I could do without reinforcement. I run the boat in a river.

 

[KurtG]

Re: Transom reinforcement

What HP does the capacity plate say the boat is rated for?

Not too many 15 fts I've seen that are rated for 90 HP.

 

[baiwan]

Re: Transom reinforcement

When I purchased the boat there were only 45 hp motors available here, There is no rating on the plate. I am scared the transom might break, and felt the same way with the 65 hp. I didn' have trouble with that
In the recommendation for boats in motor specs it says for 90 hp the boat should be 15 to 20 feet long, and 900 to 2000 lb. I reach the 900 lb gross weight with two passangers.
passangers

 

[Mark42]

Re: Transom reinforcement

A lot depends on the type of boat. Is it a jon boat or a bow rider or a deep v center console or a ski boat?

By comparison, the 16' Bayliner in my signature is rated 90 hp max. It weighs about 1100 lbs, is a deep V, has high freeboard, and knee gussets supporting the transom. The MFG is a 14', weighs about 600lbs, is a planing shallow V, and is rated 50hp max.

 

[KurtG]

Re: Transom reinforcement

That Suzuki was probably the right size for your hull. What performance issues did you have with it? What type of hull do you have (shape, material, construction)?

Photos would help people with an opinion on your transom.

fwiw, my 15' in avatar is rated for an 80 HP. I think my Hull is ~ 700 lbs (probably 900 lbs w/motor and gear- without passengers)

 

[baiwan]

Re: Transom reinforcement

It is similar to the 15 foot avatar, but is a little narrower and weighs less,
I think its 60 hp rated, I ll try to get a picture by tomorrow.
I would like to reach higher speed at times. I use the boat for water skiing mainly and 65 hp isn't sufficient I guess. First I'll have to try to fit in a picture.
Thanks.

 

[ondarvr]

Re: Transom reinforcement

You said "when I purchased the boat there were only 45hp motors available here". Where is ?here??

 

[baiwan]

Re: Transom reinforcement

Here is Bulgaria - a small country in Easter Europe on the Balcan Peninsula, surrounded by Romania, the Black Sea, Jurkey, Greece, Macedonia, and Serbia
I have a house on the Danube River and run my boat there.
I recently purchased a Johnson v-4 90 hp in poor condition and intend to repair (overhaul) it and fit it with my boat.
I have a lot of free time; have quit drinking 18 years ago and am spendind everything on boating.
Now I am looking for a reliable supplier of the spares I will need, who would agree to prepaiment and shipping the parts all the way to my country.
Meanwhile I intend to work on my boat. There is hardly any one to discuss such things around.

 

[ondarvr]

Re: Transom reinforcement

I thought that might be the case, welcome to iboats.

What year were these motors made? the 90HP may be an old one, if it is, it may have about the same power as the 65HP.

 

[baiwan]

Re: Transom reinforcement

I won't risk. I will install stailess steel pipes from the transom to beems on the bottom fo the floor. I have to open the floor any way to see the condition of the boat: it will take time.
Our season start in July a guess I will manage.
I intend to overhaul the motor; that should restore the 90 hp.

 

[ondarvr]

Re: Transom reinforcement

I don't mean the motor is worn out and down on power, before the mid 80's the HP was measured at the crank on these motors and sometimes the listed HP was a little on the optimistic side for even that measurement. Now it's measured at the prop shaft, this results in a 10 to 15% lower reading on the dyno, this can put a newer lighter 65HP motor being very close in performance to an older heavier 90HP model. That?s why I asked about the year of each motor.

 

[baiwan]

Re: Transom reinforcement

I agree! But I think it is theoretical.
I bought the Suzuki brand new in 1996 after bad experience with a 50 hp Merc. and wasn't happy with it from the beginning.
9 years later the DT 65 was stolen and I bought a 1981 50hp Johnson.
After repair it performed slightly different on my boat; 4 - 5 mph lower top speed, little less trolling power for skiing. Fuel consumption the same by the same manner of riding - when skiing - 26 mph.
That made me pick Johnson.
Anyway I have to check the condition of the boat for safety which comes first and transom reinforcement will cost me around $ 120, what do you think of the idea; stainless steel pipes from boat fastening bolts to new beams on the boat bottom.

 

[mthieme]

Re: Transom reinforcement

How about considering knee braces...similar in theory to the pipe, but more traditional and more surface area. I'm glad you are considering stringers.
Even if the transom is strong, the keel just forward could buckle over time. I have a hull in the driveway right now with this issue.

 

[baiwan]

Re: Transom reinforcement

I am checking the bottom any way. I will observe the keel and the pipes will be fit on beams running a foot away of the keel - 5 foot lond alongside it, and if nececessary longer.
I'm not familiar with the knee braces.
Boat construction is a new field for me, I'm a better mechanic.
The boat is connected with the engine I'm making.
I always consider safety

 

[ondarvr]

Re: Transom reinforcement

I must have missed the part about the 65Hp motor being stolen, I thought you still had it.

 

[mthieme]

Re: Transom reinforcement

Baiwan,
check this thread out....several different knee braces to view.
forums.iboats.com/showthread.php?t=288703
I couldn't find a fiberglass brace...same idea though.

 

[Frank Acampora]

Re: Transom reinforcement

Even on a new boat, transom reinforcement is a good investment.

Now: instead of heavy stainless pipes, why not use an aluminum angle about 5 cm by 15 cm on the top and inside of the transom for the full length of the engine opening and .080 inch or 2-3 MM plate aluminum from the transom along the inside of the splashwell?

On boats with a splashwell, the splashwell is an integral part of the transom support. Reinforcing it and tying it to the transom with aluminum is an elegant and light yet strong engineering solution to transom support. It distributes all engine thrust throughout the full hull and deck of the boat rather than concentrated at the transom.

I have a photo which I can not transfer to this site but if you want to see it, go to The Chrysler Crew. Join. Scroll down to questions. Click on it. At the upper left of the page click on photos. search for Frank's Boats. Search that album for my transom repair photos. They are of a 14 foot flat bottom boat that was originally rated for about 40 HP. I put 90 on it and later put a 125 with no problems with the transom--even at 60MPH. (80 KPH?)

 

[baiwan]

Re: Transom reinforcement

Thanks.
I think I've got someone who understands - a small boat going fast.
I'll try to find the site; knowing more makes life easier.
I picked stainless due to two reasons - difference in weight not considerable - 15 lb approximately, and welding problem alluminium welders are few, very busy and pick their job - it will take time to convince one to do it.
I am very eager to find the boat speed. That is I have to be ready for the season - beginning of July - everything done.
The transom itself was reinforced when the boat was brand new by alluminum
in the splashwell and on the outside. I am afraid the whole will be torn off the boat. I want to secure it to the boat ground - two beams - I don't trust the boat build in a small factory in a stolen "cast" and so on.
When I open the double floor things will pop up. I might as well go for a more powerfull engine and will have the reinforcement done.
The stronger the better.

 

[baiwan]

Re: Transom reinforcement

I saw the knee bracers and thing that's what I had in mind. There is a slight difference in construction - my boat is fiberglass and I have to strengthen the floor, I use stell due to technology - can't get a welder by the boat and so on. Things are moving.

 

[baiwan]

Re: Transom reinforcement

I found the correct answer: I settled the job with a proffessional at a tair price and time term, meanwhile I'll spend my time on the engine.
Learning a new job might turn out too expensive: waste of material, spoiling the boat, eventual accident and so on.