Motor weight on transom

[weezzell_5400]

I have a 1989 24' tracker party barge ....the sticker on the boat states rated for 90 up ........well currently I have a 1989 40hp evinrude on it ...and was given a 1987 120hp evinrude with tilt trim .....will the transom hold the weight of this motor ...I know that the torque and power are just as important ...but I'm not going,g to be jumping out of holes or anything ...just like going nice and easy ...and gradually build speed ...just my way of doing things lol.....but if I make a transom saver type mount for the trailer to help while towing ...I know that will help ....the wood back there is currently a 2x12 ...would I need to brace it up some how ...thanks for the input

 

[GA_Boater]

Sure. Just add a couple of chains or cables to the motor so it won't fall too far into the drink.

 

[ahicks]

I just went though this while doing a major rebuild (re-deck, carpet, furniture) and updating our engine from a 40 Johnson to a 90 Honda (4 stroke). Engine weight went from 220 or so to 380 - nearly doubling the original. Boat was rated for 140 hp

Our transom is made from laminated plywood, measuring an actual 2" thick. That was original ('99), so it was replaced.

Surprisingly enough, the rear cross member was actually bowed down with just the 40 on it! I removed that cross member, and turned it upside down, then added another cross member in back of that one. How that works out remains to be seen for sure, but I'm reasonably confident we'll be OK.

I would not trust a transom made from an actual 2x12.

 

[jbcurt00]

Yeah, w an OB thats 33% over rated hp, what could possibly go wrong w an aluminum pontoon rated for a 90......

 

[HotTommy]

Weezzell,
There is no way to give a worthwhile answer based on the limited information you provided. But the age and rating given by the manufacturer says no. If you can sufficiently reinforce the transom, engine pod and sturucture it mounts to, then likely yes. .... Let me address one misconception you mentioned regarding the effect of the thrust produced by the engine. Regardless of how slowly you reach full throttle, the engine will be producing its maximum thrust there. The reason a boat doesn't go any faster at that point is that the drag produced by the boat equals the thrust of the motor. The maximum stress on the transom/pod occurs when those two forces are at their peaks. I suppose a rapid acceleration could produce a momentary higher peak stress, but running at full throttle is very stressful in itself.

 

[weezzell_5400]

Man I didn't know that there were so many people on here that just like to be insulting ..and sarcastic....I'm pretty new to boating and don't know to much about the subject at hand ....I had plans on changing out the wood at the back to some marine grade plywood that I have and doubling up on it and glueing it together with some 3m 5200 that I have ....maybe even triple ....the pontoon logs that are on the boat are 22inch and the transom aluminum is 1/8 inch thick ...ill post some pics in a few mins of the transom

 

[GA_Boater]

It has nothing to do with insults.

Engineers and the Coast Guard have very good reasons for the labels giving max horsepower and passengers. You can do anything you want and hang any motor on the toon, but few of us will agree that it is a good idea.

You have two strikes - Too much weight and too much power. Don't get cranked at us for not saying to go for it when you asked for advice. Motor pods on toons give up the ghost, even when properly powered. Facts are facts.

 

[weezzell_5400]

No Title

 

[HotTommy]

Weezzell,
The comment about the chain was not entirely sarcastic. When I went to a bigger motor and a new engine pod on my old pontoon boat, I secured it with a cable for the first season because I wasn't sure how well made the pod was. When you do something to an old boat that it was not originally intended for, you need to take precautions. .... If you decide to do this project yourself and you are not expert at structural engineering and marine design, then you are taking a risk. Lots of us do it, but you'd be wise to go heavy on the reinforsement if you want to run your over-rated motor. Here are the places that likely need strengthening:

• The transom (wood piece that the motor bolts to): New wood, thicker wood, high quality wood and glue, and an aluminum backing plate would all help.
• The engine pod where it supports the transom: This aluminum piece takes lots of stress as the bottom of the motor is pushed forward by the prop causing the transom to try and rotate aft at the top. The motor rating on your boat was based in part on the strength of this piece. You may need to have additional aluminum corners and/or gussets welded into your motor pod.
• The engine pod where it mounts to the logs: Some of us have sourced and added additional cross beams between the logs to support the pod. These are most important toward the aft end of the pod.

If this seems like too big a project, then perhaps you can locate a replacement pod that was intended for a larger motor. I found one at a pontoon boat salvage yard nearby. Then the only task is removing and replacing the old pod with plenty of cross beam support.

 

[ahicks]

If this 120 is about the same weight as the 85/88/90 hp engine, you might have that going for you. I'm not sure where the break is where the weight jumps significantly - to a level that's likely not worth considering.

I do see the water line on the toons is pretty high, getting up high enough where I would be shy about adding much weight. Is the boat set up where some of your normal load can be removed or possibly shifted forward?

The pics look like you (or somebody) have installed a planked deck. That's pretty unusual, was wondering how it's working out? It's a little concerning regarding your question here, as it would offer nothing in the way of support for the engine pod - like 3/4" ply would. The cross members are pretty much on their own. This alone might cause me to consider beefing the structure up - even without the effects a heavier more powerful engine might add to the picture.

 

[MH Hawker]

weezzal bear in mind that this is a international forum with a bit over a hafe million members and it consist of people who have devoted their lifes to this and their extremely safety oriented, now this time of year a lot of new people ask questions and get pissed because its not the answer they wanted

 

[weezzell_5400]

Ok well I been doing some reading ...and I found out that the 40hp currently on the boat weighs about 190 lbs....and the sticker states is good for up to 90hp ...of the same year as the boat a 90hp motor weighs in at 300 lbs.....and the 1987 120hp weighs in at roughly 370 ....so is that really going to make a big differance ........also looking at the newer evinrude 90hp they weigh from 320 lbs to 405 lbs ......and I'm not mad ...please don't take it that way.....I'm just trying to learn ....I am still wearing arm floaties when it comes to boating and the whole logistics behind some of it ....thanks again

 

[jbcurt00]

Wieght isnt the only limiting factor, 33% overpower is, jumping from a 90 to a 120hp.

Look around, olenty of why is my 'toons transom/mount cracked, broken, pulling away? topics.

Even on boats that have an under rated motor on them.

Ya asked if it was a good plan to overpower your toon, the reply was no, several different ways.

As a novice boater, its a common question, and if for no other reason then you're a novice boater, the answer is no as well.

 

[HotTommy]

Speaking solely of motor weight, one way to see how a 400# motor will affect your boat at rest in the water is to ask a 210# friend to perch on top of your current motor. You'll see that its not just the amount of weight, but the fact that it is located way back from the center of the boat. .... BTW, a previous forum member complained because his 20' boat was too heavy in the back because everything but his wife was in the back. We recommended his wife gain weight.

 

[ahicks]

I see too much in the way of negatives here that would need to be overcome. Stiffness of the floor and existing weight of the boat are the biggest factors.

If the boat were riding higher in the water (lighter) you could do some backyard engineering to stiffen things up to handle what I feel is a significant weight increase, and thus maybe some increase in it's ability to handle power. The problem is, those mods add weight as well. With the additional weight of the mods, and the engine, thinking the end result would not be very sea worthy (WAY too heavy for those pontoons).

With enough skill, determination, and MONEY, you might be able to get this to work out. Converting to tri-toon might be the easier way out here.

 

[weezzell_5400]

I'm just trying to undestand something ...the boat rated at 90 no....the weight and torque of the 1987 evinrude 120hp on the boat ....what would be much differant than me putting on a brand new 90 hp evinrude that weighs in at 365 ish ...and the 1987 evinrude weighing in at 370ish ....and the newer motor probably having the same ammount of torque as the older 120 ....see this is where I'm having trouble understanding

 

[GA_Boater]

Let's put it like this;

If something bad happens to the point of lawyers getting involved and they find out the boat is overpowered, it makes your defense much more difficult.

 

[HotTommy]

Weezzell,
The essence of your argument is that your boat was rated for 90 HP years ago and a modern 90 HP has about the same power as an old 120 HP motor. If you're going to use the old motor, you need to use the old rating limit that was suitable for engines of that era. If your argument holds, then you should limit your choice of modern engines to only 75 HP as they produce about the same power as an old 90 HP.

The legal argument is valid but it comes down to risk tolerance. I don't think you're going to get anyone here to agree on the record that its a good idea to exceed the rated engine power, especially if you don't do anything to modify the boat to handle the added weight and power. You've been offered the following suggestions:

1. Don't do it.
2. Modify the boat to make it safer.
3. Do what you want and live with the consequences.

I think its time to pick one.

 

[ahicks]

I'm just trying to undestand something ...the boat rated at 90 no....the weight and torque of the 1987 evinrude 120hp on the boat ....what would be much differant than me putting on a brand new 90 hp evinrude that weighs in at 365 ish ...and the 1987 evinrude weighing in at 370ish ....and the newer motor probably having the same ammount of torque as the older 120 ....see this is where I'm having trouble understanding

The part you need to understand is the boat is already floating low, very likely much lower than when it was originally built. Fix that issue, bring this back up again, and you may see different input - from me at least. I for one, will never endorse adding weight to a boat already floating low in the water....

I have no concerns regarding doubling or tripling a boats rated power - IF - it can be done in a safe manner! This has nothing to do with what the boat was rated for 30 years ago. That rating is a guideline derived from engineering data. Those same guidelines can be used on a boat whose engineering data has been changed (e.g. cross members added, engine pod redesigned, etc.) to establish a much higher rating.

 

[weezzell_5400]

No Title

The water line that you are seeing in the pics is from the previous owner ....he had it tied up at the dock at his house and had all kinds of decking boards on it from redoung his dock and had tools and dock furniture all on the boat for months ...he used the boat as a sort of storage area ....so the boat does not actually sit that low in the water ....and as far as adding a 3rd log to make it a tritoon ...it already has a short 3rd toon in the front ...its 6 foot long from tip to back and they are 22inch logs