Extending trailer to brace engine

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Sheppie62
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Sailboat: MacGregor 26X
Location: Mission Bay San Diego

Extending trailer to brace engine

Post by Sheppie62 »

I’m adding a heavier 90hp Yamaha motor to my 26x, the Yamaha needs a little more space for clearance to tilt forward. I’m adding setback spacers and reinforced the Transom with 3/8” aluminum plates. My concern is while trailering the motor may put stress on the transom. I’m thinking about extending the trailer all the way to the back of the boat so I can attach an engine brace while towing. Also thinking with the increased weight from motor and the trailer extension, I could just add an axle behind the original axle. My tow vehicle is a Dodge Ram Van 3500 1 ton. Any thoughts on how this would work out? Any reasons not to do it? I am fully capable of the fabrication/and believe I could this strong enough to last.
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Sheppie62
First Officer
Posts: 351
Joined: Thu Sep 28, 2017 1:04 pm
Sailboat: MacGregor 26X
Location: Mission Bay San Diego

Re: Extending trailer to brace engine

Post by Sheppie62 »

I believe the added axle would get welded or bolted onto original portion of frame, drawing seems not to scale.
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Tomfoolery
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Sailboat: MacGregor 26X
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Re: Extending trailer to brace engine

Post by Tomfoolery »

Sheppie62 wrote: Tue May 11, 2021 8:05 amI believe the added axle would get welded or bolted onto original portion of frame, drawing seems not to scale.
Ha ha not even close to scale. I made that sketch to illustrate the reason the Mac Bump® is employed.

The OP can use this one, which is to scale.


Image

Though personally, I wouldn't bother. Tilt it up all the way, where it's almost balanced, and drive.

When motoring fast, my 50 hp exerts almost 600 lb thrust force at the prop at WOT and 16 mph, and a 90 would be nearly double that. Both cases assume a mere 50% efficiency on prop shaft hp, though I think it's typically a bit better than that which would increase that force number, the rest going to churning water and making it warm.

The dead weight of the OB is still there, of course - that's just the horizontal force at the prop center. That's waaaaay more than the force (dead weight is the same) and moment (almost zero) exerted on the transom with the engine tilted up full and just bouncing down the road on a trailer.
Tom
Be seeing you . . .
Sheppie62
First Officer
Posts: 351
Joined: Thu Sep 28, 2017 1:04 pm
Sailboat: MacGregor 26X
Location: Mission Bay San Diego

Re: Extending trailer to brace engine

Post by Sheppie62 »

Image
Yes that picture is much better, I have a 10” setback with a lift jack on the 377 LB. motor, so a little more leverage than straight on transom. Do you think I could put new axle behind the original without the frame extension?
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Tomfoolery
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Re: Extending trailer to brace engine

Post by Tomfoolery »

Sheppie62 wrote: Tue May 11, 2021 10:44 am Image
Yes that picture is much better, I have a 10” setback with a lift jack on the 377 LB. motor, so a little more leverage than straight on transom. Do you think I could put new axle behind the original without the frame extension?
It looks like you could*, though that would add tongue weight. That pole tongue isn't designed for more than about 350-400 lb tongue weight, so to be safe, I would reinforce it. But in your favor, the heavier engine, mounted further back, will offset that to some degree.

You can measure your spring bolt to bolt distance (spring effective length), add about 8" for the equalizer, and from the rear spring eye on the existing spring measure back that distance to see if the back end of the new spring would be on the trailer. I think the original was about 26" long, but again, that's from memory.

Also have to check for the ability to add fenders, as the goal post may be in the way.

*from here, but I'm not where I can verify.
Tom
Be seeing you . . .
Sheppie62
First Officer
Posts: 351
Joined: Thu Sep 28, 2017 1:04 pm
Sailboat: MacGregor 26X
Location: Mission Bay San Diego

Re: Extending trailer to brace engin

Post by Sheppie62 »

I measured another trailer with tandem 5 lug axles. And if I put 2nd axle behind the original, the trailer would extend 20” past the rear hanger bolt. To the back of boat would be about 56”. Maybe it would be best to get the new motor mounted (when it comes in, it’s on order) then see how much tongue weight it will have.
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Tomfoolery
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Re: Extending trailer to brace engin

Post by Tomfoolery »

Sheppie62 wrote: Tue May 11, 2021 6:04 pm I measured another trailer with tandem 5 lug axles. And if I put 2nd axle behind the original, the trailer would extend 20” past the rear hanger bolt. To the back of boat would be about 56”. Maybe it would be best to get the new motor mounted (when it comes in, it’s on order) then see how much tongue weight it will have.
I'm not sure what you're saying, but FYI the second axle on my trailer was added after moving the original forward. The mid-point between the axles is where the original single axle was, before the modification.
Tom
Be seeing you . . .
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