How to Reinforce Transom ???

[bighermHK45]

Since I will be installing a heavier outboard (going from 40HP to 115HP), what/how can I reinforce the transom to account for the additional weight and torque? I don't have access to an aluminum welder, so I was thinking of installing brackets or braces of some sort to attach to the deck support beams or deck itself. Looking for ideas before I install the 115HP.

 

[gm280]

First of all, we need to know what type boat and pictures would be a great way to provide that as well. Swapping from a 40HP to a 115HP is a huge upgrade. Is your boat capable of handling that high a HP rating? If your boat is capable then your hull and transom should be as well. The fact that you are talking about increasing the transom support leads me to believe this will by beyond the max recommended manufacture's plate specs. Post some pictures for everybody to see...

 

[bighermHK45]

The Misty Harbor 2424CC pontoon is rated for the 115HP. I don't want to take any chances and would rather reinforce it now while I have the motor off. I will try and get pics today after it stops snowing....

 

[HotTommy]

I don't know anything about your particular boat, so take what follows with a large grain of salt. .... When I went to a much larger motor on my pontoon boat, I both replaced the engine pod and added additional supports for it. Both engine pods attached to the rest of the boat by bolting to the cross members that run from log to log and support the deck. To add supports, I measured the space needed for the original cross members and bought aluminum angle that was the right size to fit (e.g., 2"x2"x1/4" and 8' long). I inserted the additional supports and bolted them to the logs and the engine pod. They provided additional strenght for both the weight and torque of the motor.

 

[bighermHK45]

I don't know anything about your particular boat, so take what follows with a large grain of salt. .... When I went to a much larger motor on my pontoon boat, I both replaced the engine pod and added additional supports for it. Both engine pods attached to the rest of the boat by bolting to the cross members that run from log to log and support the deck. To add supports, I measured the space needed for the original cross members and bought aluminum angle that was the right size to fit (e.g., 2"x2"x1/4" and 8' long). I inserted the additional supports and bolted them to the logs and the engine pod. They provided additional strenght for both the weight and torque of the motor.

Do you happen to have pictures of your modifications? It sounds like you did what I have in mind. I will post pictures of my transom here shortly.

 

[bighermHK45]

... Post some pictures for everybody to see...

 

[bighermHK45]

 

[HotTommy]

I'm away from home today, but I'll post pictures when I can. ..... On thing I had to consider was the physical size of the larger motor. My original engine pod tucked the motor in close to the boat, under a raised deck at the very back. The bigger motor was so tall it would it could not be tilted up without hitting either the deck above or the fence in front of it. So I swapped to a stronger engine pod both to support the bigger engine, and so I could move the transom about a foot farther back. I also modified the height of the transom so I could get the engine at just the right height to fit in the tight space.

The original engine pod was bolted to crossmembers that ran the full width of the boat. The most aft crossmember was located about 15" forward of the front of the original engine. When I moved the new engine pod aft about a foot, I had room to place two new crossmembers aft of the last original crossmember. If you plan to use your existing engine pod, you may want to slide one or two additional crossmembers in between the existing ones. The easiest way for me was to remove the trim piece that wraps the boat at the deck, and slide the angle aluminum in from the outside edge. You'll want to check for obstructions (e.g., throttle cable, wires, etc.) beforce deciding exactly what to do and which side to enter from.

 

[HotTommy]

I found this photo that may help you understand my earlier description. This is the original engine and pod. The deck above the engine is temporarily raised in this photo.


Disregard the link below. It is an artifact of my inability to remove a bad link.

 

[bighermHK45]

Thanks for posting the picture and description. Looking forward to seeing your setup. Mine looks reinforced to accommodate the 115HP, especially considering some of the pictures I have seen of other engine pods that have no angle aluminum included. I would like to bolt a brace/bracket from the top of transom to the first deck crossmember to help keep the transom pulled forward and not have the welds support all of the weight. All my welds are in tact but the pontoon only had the 40 HP since new. I am nervous installing the 115HP....

 

[GA_Boater]

Your pontoon was designed to handle the weight and power of a 115, so why are you worried? You know if you add stuff incorrectly or in the wrong place, you may actually weaken the structure.

Since you are concerned about weight, what is the weight difference between the 40 and 115?

 

[lmuss53]

I'm with GA Boater on this. If the boat is rated for the 115 I would inspect the factory transom and pod and if everything looks OK, hang the motor on and go for it.

 

[MTboatguy]

If it is rated for a 115 and you don't have any damage back there, I don't see why you would be worried? Have you noticed any damage? I would say, you are in pretty good shape if no damage is apparent, if you have been running a 40 on a boat designed and rated for a 115, then you have not put any stress on it over the time you have had it. It should be good to go, hang and go play.

 

[HotTommy]

bigherm,
If your boat is rated for the engine you want to use and it appears in good shape, I tend to agree with the others about using the engine pod as is. I HAD to change for the reasons mentioned above. .... BTW, hanging a couple hundred pounds more on a system of welded and bolted aluminum shouldn't be a big deal. The bigger challenge is having the transom/engine pod withstand the much greater torque applied to it by the more powerful engine. Propellers push forward near the bottom of the engine, but the engine is attached up high at the transom. That means the running engine is trying to twist the top of the transom backwards while pushing the bottom of the transom forward. If I were worried about about my transom/engine pod, that is where I'd want to see it reinforced.

 

[bighermHK45]

Your pontoon was designed to handle the weight and power of a 115, so why are you worried? You know if you add stuff incorrectly or in the wrong place, you may actually weaken the structure.

Since you are concerned about weight, what is the weight difference between the 40 and 115?

The 40HP is 185lbs and the 115HP is 348lbs. So the new motor will almost be twice as much weight. Combine that with the extra torque and that is why I want to secure the transom the best I can.

Not sure what you mean by weakening the structure if I reinforce it. Any braces would be there to supplement and not be installed to create extra pressure on the welds. If you have some examples of what you are referring to, please share.

 

[HotTommy]

Here's an example. If you drill a hole to bolt something new in place, the piece you drilled may be weaker because of the hole.

 

[HotTommy]

As you are concerned about the strength of the transom, I had one more thought that might apply here. The photo of the transom itself showed it entirely encased in aluminum plate. My guess is that there is a wooden core inside. It will become obvious when you remove the old engine and can see inside the mounting holes. While the aluminum looked OK, it is possible that the wooden core has deteriorated some. If this were my boat and I found a wooden core, I would remove the top cover (it appears to be held in place with some rivets) and inspect the core. If you decide to replace it, keep the old one as a pattern until the new one fits right.

 

[lmuss53]

The guys who designed and built your boat did all the figuring and building necessary for you to run a 115 on it Aside from what Tommy pointed out above, the wooden core possibly being rotten, there should not be any issues with your transom, I would not do anything at all to try to improve it.

I know it goes against all the rules, but I ran a 90 HP OMC motor on my Forester which is rated for a 60 for most of a Summer with zero negative issues. I took the 90 off only because I thought the added performance didn't justify the added fuel consumption and cost. That transom. overpowered by 50% never showed any sign of weakening, cracks, warping or any sign of wear or damage. It is still fine 5 years later.

Hang your motor and go enjoy your boat.

 

[bighermHK45]

As you are concerned about the strength of the transom, I had one more thought that might apply here. The photo of the transom itself showed it entirely encased in aluminum plate. My guess is that there is a wooden core inside. It will become obvious when you remove the old engine and can see inside the mounting holes. While the aluminum looked OK, it is possible that the wooden core has deteriorated some. If this were my boat and I found a wooden core, I would remove the top cover (it appears to be held in place with some rivets) and inspect the core. If you decide to replace it, keep the old one as a pattern until the new one fits right.

Replacing the transom core is a good idea. I noticed the wood was watersoaked when I dropped the original motor down one hole on the transom. Any suggestions on what to use for the new core?

 

[lmuss53]

I used exterior grade plywood for the transom in my Sea Nymph sealed with exterior poly coating, I think two pieces of 3/4 and one of 1/2 to give me the 2 inches required. I glued it all together with liquid nails, You can do any number of things to preserve it from painting to epoxy encapsulation. I figured if nothing at all was OK for the factory, the poly sealant would be OK for me. I would use exterior grade plywood with a good coat of outdoor paint or epoxy on it.

For your original wet is OK, punky, soft. delaminated, obviously rotted is not. OK really is OK to find.