Transom stress concerns with bigger motor

[Wood_Duck]

I currently run a 1546 Roughneck with 30/25 4stroke Merc. I'm planning on upgrading to a 60/40 although it's rated for a 25hp. I'm good on insurance but looks like with the exception of mercury everyone just offers a 60 with 20" shaft. In the event I go with say yamaha, I'd be forced to either add a jack plate or have a 25" transom fabricated. I'm not sure how concerned to be about adding an additional 80ish pounds on the transom and them a jack plate. Any thoughts with this?

 

[earl60446]

Why do you need a 25" transom for a long shaft motor (20")? In any case, I think you should be concerned about putting a 60 on a transom rated for a 25 because the transom could fail structurally. Refabricating the transom to 25" might make it strong enough (if done right) but a 1546 seems too small for a 60. Plus the DNR might see it as a violation. Heck, my boat is 16ft and 72" wide at the transom gunnel and is rated for a 60, although not a jet boat.
Tim

 

[Wood_Duck]

earl60446 » 58 minutes ago[/url]"]Why do you need a 25" transom for a long shaft motor (20")? In any case, I think you should be concerned about putting a 60 on a transom rated for a 25 because the transom could fail structurally. Refabricating the transom to 25" might make it strong enough (if done right) but a 1546 seems too small for a 60. Plus the DNR might see it as a violation. Heck, my boat is 16ft and 72" wide at the transom gunnel and is rated for a 60, although not a jet boat.
Tim

20" motor with jet pump will need a 25" transom for correct height. Still looking like Mercury is the only option in a new 60/40. It will be around 80ish extra pounds vs the 30/25. It's really not going to be that extreme. With a 60/40 it'll likely still be slightly slower than a 25 prop. Those capacity plates are more suggestive and basically no one will be taking issue to it. Just the transom concern. I'd rather just add a couple braces for a 15" motor than have a big riser fabbed for a 20"

 

[great white]

Not sure about where you live but the capacity plate is just a bit more than a suggestion where I live. Get caught over capacity and they take a very dim view of it. Big motor on a little tinny is usually a dead giveaway to pull you over and have a closer look.

Just sayin...wouldn't want you to get "pinched" after putting all that work into it.

 

[Wood_Duck]

I see it quite abit around here. And it is only "15" horsepower over my 25hp rating, hah. I'm gonna try and call lowe and see if they can provide a transom rating in terms of weight capacity

 

[acabtp]

Wood_Duck » 41 minutes ago[/url]"]I see it quite abit around here. And it is only "15" horsepower over my 25hp rating, hah. I'm gonna try and call lowe and see if they can provide a transom rating in terms of weight capacity

there is no chance that lowe will tell you that putting anything more than a 25 on there is ok. that would totally open themselves up to liability if you hurt yourself or someone else.

you should go over to https://www.gpo.gov/fdsys/pkg/CFR-2002-title33-vol2/pdf/CFR-2002-title33-vol2-sec183-43.pdf and take a look at the actual law and formula for calculating outboard capacity. they are not suggestions. since your boat is a 15' it is not eligible for special consideration and a performance test to determine the limit; it must use the listed formula, so the only way to increase your limit would be to make the boat longer, widen the transom, or make the transom more than 20" tall and add remote steering (if it's not already).

yeah, it would be def be fun, but so is running no exhaust and drag slicks on the street. similarly, it's an easy excuse for any cop/ranger/coastie to give you the hassle of a ticket whenever he felt like it (assuming he doesn't beach his boat trying to catch you haha).

 

[Wood_Duck]

Ok basically I don't care about the capacity plate. I can buy a motor and get insurance so I'm happy with such. Nor am I calling Lowe to specifically ask about hanging a 60/40. I'm merely inquiring if they have a set "weight" they consider a limit for the transom. No mention of horsepower capacity. There's no boat nazis roaming around here. Just looking for any thoughts on transom integrity/bracing required.

 

[earl60446]

Have no idea on set "weight", you will likely be ok but your gonna do it anyway so might as well get started.

In the immortal words of Captain Ron
Martin Harvey - We don't know if it's safe.
Captain Ron - We'll find out on the ocean, anything's gonna happen, it's gonna happen out there.

Tim

 

[Wood_Duck]

That's the spirit lol. I've saw a couple with 23hp surface drives which are only about 40ish lbs less than a 60/40. My thoughts are when I go to have the flotation pods welded on, to just add a couple thick walled tubular braces from the top of the transom to the rear deck.

 

[crazymanme2]

Brace your transom to the side of your boat,very strong.I built extra beefy corner gussets for mine.

 

[typed by ben]

i personally would be concerned with torque being applied in all the wrong places. itll be greatest at the top of the transom, which will already be nearly twice as tall as it was designed to be. your motor will be heavier and youll be applying thrust from the end of a moment arm again twice as long as the boat was designed to carry.

any redesign you do is going to have to be MASSIVE and tied back to the hull in such a way as to resist the torque applied to the top of your transom.

 

[Wood_Duck]

typed by ben » 42 minutes ago[/url]"]i personally would be concerned with torque being applied in all the wrong places. itll be greatest at the top of the transom, which will already be nearly twice as tall as it was designed to be. your motor will be heavier and youll be applying thrust from the end of a moment arm again twice as long as the boat was designed to carry.

any redesign you do is going to have to be MASSIVE and tied back to the hull in such a way as to resist the torque applied to the top of your transom.

What do you mean by twice as tall? It's currently a 20" transom as is. I'll only be raising it most likely if I go with a 20" shaft motor which would be the yamaha. The mercury I can get the same 15" shaft that I currently have. If that's what you mean.

 

[typed by ben]

Wood_Duck » Today, 15:31[/url]"]

typed by ben » 42 minutes ago[/url]"]i personally would be concerned with torque being applied in all the wrong places. itll be greatest at the top of the transom, which will already be nearly twice as tall as it was designed to be. your motor will be heavier and youll be applying thrust from the end of a moment arm again twice as long as the boat was designed to carry.

any redesign you do is going to have to be MASSIVE and tied back to the hull in such a way as to resist the torque applied to the top of your transom.

What do you mean by twice as tall? It's currently a 20" transom as is. I'll only be raising it most likely if I go with a 20" shaft motor which would be the yamaha. The mercury I can get the same 15" shaft that I currently have. If that's what you mean.

sorry, didnt see where you stated what your current transom is and assumed you had a 15".

 

[Djknyork]

I think there's a few pictures floating around, maybe on the jet forum, that show what you're looking for. You WILL want to strengthen your transom and you can do that by adding larger corner gussets. Or by stretching a brace from your transom up the sides of the boat pretty far.