Raising transom on 2015 Alum. boat

[Seahawk170]

Hello, I'm a newbie here and would appreciate some advice from those that have successfully raised the transom on an aluminum runabout. I like to fish Puget Sound (saltwater), and during my 10 +/- trips last summer I hated seeing following waves occasionally splashing into my transom well. While at a marine store a few weeks ago I talked to a local machine shop owner who told me that he has raised well over 100 transoms over the years and was sure he could raise mine up to handle a 25" outboard. He mentioned a new aluminum plate fastened to outer transom with (3) 1/2"x1.75" alum.bars vertically welded to top of my notched transom, plus a new welded plate across the top with a new plate welded to it all on the motor well side. This machinist also said that he would need to physically see my boat for measurements, and perhaps a different method will be required.

My boat is a 2015 Riverhawk, Seahawk Sport 17' (Oregon made), and it currently has a 20" transom height where outboard mounts, 14 degree deadrise aft, sides of boat are 34",and bottom width is 66". The outboard sits in a notched transom (16" bottom to 26" top width at notch), and then the secondary top of transom is 5" taller. There is no wood in my transom, it's all aluminum, and according to spec. has a 0.160" transom skin, reinforced with semi-box beam aluminum struts vertically all welded.

Does the above method for raising the transom notch seem reasonable, and is there any major structural issues I should be aware of?
Last weekend I purchased a 2013 Yamaha 90hp engine with a 25" leg, but it's 381# weight has me very concerned about structurally getting this done properly.

All advice is greatly appreciated!!
Thanks,
Arne

 

[jbcurt00]

Buy a 25in transom boat

 

[fhhuber]

Best to get a boat built for what you want rather than redneck modifying to make it work.

You need triangulated support brace(s) coming forward and down from the top of the transom when you raise it or you'll be imposing loads on the corner joints that the hull wasn't designed for.
Some hulls come with triangulated braces from the factory... (See the Crappie Deluxe in this slideshow of boat pictures alumacraft.com/About-Alumacraft.php?content=boat_models)
Better to have a stronger brace system than needed than not enough.

 

[Mikeopsycho]

This is something I have considered doing on my Quintrex 12 1/2' aluminum boat for the same reasons, and I see no reason why it wouldn't work, provided enough bracing is added. My particular boat comes in a short or long transom model. I bought the short transom one because I already had a Honda 15 short leg outboard. Another option might be to add a generous plashwell with drainage scuppers. Got pics?

 

[64osby]

I hated seeing following waves occasionally splashing into my transom well.

How often in ten trips?

Would 5" of extra height solve the issue?

This is what a splash well is design for.

Are you trying to solve a pet peeve or resolve a safety issue?

If it is a safety issue, I would look at a bigger boat.

 

[Seahawk170]

Best to get a boat built for what you want rather than redneck modifying to make it work.

You need triangulated support brace(s) coming forward and down from the top of the transom when you raise it or you'll be imposing loads on the corner joints that the hull wasn't designed for.
Some hulls come with triangulated braces from the factory... (See the Crappie Deluxe in this slideshow of boat pictures alumacraft.com/About-Alumacraft.php?content=boat_models)
Better to have a stronger brace system than needed than not enough.

Thanks, this is the type of input I was hoping for. The splashwell on my boat runs the entire width, so now you have me strongly considering to add a couple of aluminum struts to virtually eliminate any top flex. This boat's construction is very solidly built as-is, (hull weighs 1175 lbs), and the thinnest aluminum is 1/8" so don't think that a mere 5" raise should affect it's corner joint's structural integrity. Its not easy for me to describe exactly how the transom, well, and 5" wide gunnel ties together, but to me it looks very strong and would take a lot of punishment to break at it's corners.

Thanks again for the added brace support suggestion, and will definitely discuss it with the machinist.

 

[Seahawk170]

This is something I have considered doing on my Quintrex 12 1/2' aluminum boat for the same reasons, and I see no reason why it wouldn't work, provided enough bracing is added. My particular boat comes in a short or long transom model. I bought the short transom one because I already had a Honda 15 short leg outboard. Another option might be to add a generous plashwell with drainage scuppers. Got pics?

Sorry,no pictures yet. My boat is currently parked in my shed and backed all the way in.. (too dark in there). I plan on taking my boat down to the machinest this Saturday for his measurements and to discuss my options, so I plan on taking pictures at that time.

 

[Seahawk170]

How often in ten trips?

Would 5" of extra height solve the issue?

This is what a splash well is design for.

Are you trying to solve a pet peeve or resolve a safety issue?

If it is a safety issue, I would look at a bigger boat.

I understand your point, and the occasional wave only comes over while trolling along in a following 3' sea, so guess its just something that bugs me.
A bigger boat would be nice, but that would require a bigger truck and boat shed. My S-10 with it's 4.3 liter engine is pushing it's limits now. ;-)

 

[ondarvr]

Two things,

1. The transom can be raised easily and it's done frequently in this part of the country.

2. If your only concern is a little water coming into the splash well every now and then, well, get over it, it's not an issue.

Higher transoms are rarely a bad thing, but they are only needed when you actually do require one, and you don't. If it bothers you enough to do it, there is no downside other than the cost.

 

[Seahawk170]

Buy a 25in transom boat

But then I'd have to go in debt. In my mind this boat's transom design should never have been notched by 5".

If xxxxxx's did not have an 18' Duckworth w/25" transom (a very similar style boat), then my modification plan wouldn't have happened.
Going ahead with my plan might prove regrettable, but I'm afraid if I don't then I'll regret it even more.

 

[Seahawk170]

ondarvr, thanks for the reply.

One thing I forgot to mention is that my boat currently has an older 70hp 2-cycle Yamaha which weighs in at 228#, plus I have an old 6hp 2-cycle trolling motor.
Together both of these engines weigh in at about 290 lbs. Literally all of the 4-cycle engines in the 90 hp range are nearly 400 lbs, so the waves-to-well event will become too familiar for comfort while out fishing next season. Even the 90 hp Etec weighs in at 320 lbs, but I wanted a quiet 4-cycle outboard that I could also troll with without the risk of fouling plugs at near idle speed.

Thanks for the positive encouragement.

 

[64osby]

You stated the hull was a 2015 model. Does it have a warranty?

If you modify the hull will it void the warranty?

 

[Seahawk170]

You stated the hull was a 2015 model. Does it have a warranty?

If you modify the hull will it void the warranty?

It is a 2015 boat, so I suppose this modification will definitely void it, but to me its still a better choice than selling it and losing 1/3 of what I paid.
Then I'd need to buy another boat and need to lay down another 15k or so. ;-) My new boat is well built so I doubt I'll ever have a problem with her hull.

The main reason I bought this boat is because my right hip is badly arthritic so my motorcycle summer touring days are off until I get a full hip replacement. My previous boat (17' Bayliner) was to be my summer's recreation but the plywood in it's transom was shot, which I discovered this after buying a used 70hp Yamaha outboard for it. Then after looking at a lot of boats, I settled on this 17' Riverhawk from ******** last June, since they would sell me just the boat without an outboard or trailer.

So now I've decided that I'd just like to feel a little safer while fishing a couple miles offshore in this little runabout. A rogue wave over it's present transom looks to me like it could easily add a fast 150# of immediate weight, before it's 2 small drain holes would drain it and the next average sized wave were to hit.

Thanks for the warning though, I actually didn't even give it a thought thoughout my planning process. LOL

 

[64osby]

Have you looked at any splashwell shields? Back trollers seem to like them.

 

[Watermann]

:welcome: aboard Seahawk!

I've fished in 10' Jon boats, 40 ' offshore boats and about everything in between. They are all scary when the conditions are right so what comes into play is the man behind the helm. The good skipper recognizes sea conditions and knows his boats weaknesses and all have some, there's no perfect boat. Be aware and adapt to the conditions and chances are you won't have anything to worry about. In the case that worries you, don't let following seas overtake you rather stay on top of them and fish bow into the whitecaps.

A 17' River boat isn't designed to be an offshore big water boat so when it gets really ugly head back to port like a good skipper even if you have a transom modified by bubba at the shop. :joyous:

 

[GA_Boater]

:welcome: aboard Seahawk!

I've fished in 10' Jon boats, 40 ' offshore boats and about everything in between. They are all scary when the conditions are right so what comes into play is the man behind the helm. The good skipper recognizes sea conditions and knows his boats weaknesses and all have some, there's no perfect boat. Be aware and adapt to the conditions and chances are you won't have anything to worry about. In the case that worries you, don't let following seas overtake you rather stay on top of them and fish bow into the whitecaps.

A 17' River boat isn't designed to be an offshore big water boat so when it gets really ugly head back to port like a good skipper even if you have a transom modified by bubba at the shop. :joyous:

I feel this is the best post in the thread. Know you and your boats limitations!

Voiding the warranty was mentioned, but on the other side - What about resale value?

 

[ondarvr]

I didn't look up to see what HP you boat is rated for, but I assume 90 or more HP. If it's rated for that, then the weight is fine, you're stressing over a perceived issue, not a real one.

I have boated on Puget Sound for more than 45 years in every size boat imaginable, not one of the outboards I owned had a transom taller than 20", and I can't remember a time where it caused a problem. I even lived on the water for many years, we had boats of a similar size moored out front all summer, some had 20" transoms and no splash wells. Your type of boat is used throughout the NW on all waters and you are the first person that has expressed such an extreme concern about the 20" transom.

Try the splash guards that were mentioned earlier, they're cheap and easy and achieve about the same thing. I think I would have held off on buying a 25" motor until you made the commitment to raising the transom. As for raising it, I have no concerns about it working well, if you are worried more about the height than the warranty, and it sounds like you won't sleep at night without raising it, then do it.

 

[Seahawk170]

ondarvr, my boat's capacities plaque states a 90hp recommended motor. The web site & my brochure states 140 to 200hp, although anything larger than a 90hp would be extreme overkill for this small boat. My thought is that with the added weight of the 4-stroke 90hp, my transom will sit that much lower in the water. Then if I later want to add a 6 or 8hp kicker motor, the waves will become even more likely to breach over.

My thoughts on raising my transom to 25" might be overly cautious, but it'll certainly make me feel better when I'm miles from shore and the northwesterly winds kick the chop up to 4+ feet. Also I'm now committed to raising it since I just bought that 90hp. ;-)
Thanks for the feedback, and good reasons to possibly change my mind.

 

[Seahawk170]

I feel this is the best post in the thread. Know you and your boats limitations!

Voiding the warranty was mentioned, but on the other side - What about resale value?

In my mind it's resale value should be improved.
My plan is to keep this boat throught my remaining years, and then my wife can dispose of it however she pleases. ;-)

 

[Seahawk170]

Have you looked at any splashwell shields? Back trollers seem to like them.

I initially was considering that route but concluded the only permanent solution is going taller.