HP Rating for a custom bracket

sasqman

sasqman

Crew Member
Hi all,

Now that I'm looking at a repower with a new motor I need to get my custom bracket rated for horsepower to keep the warranty people happy. Anyone know any structural marine engineers that would sign off on it. I will have the boat out of the water next week to get more accurate measurements.

Here is a pic. Its on the boat right now holding my 115hp merc and preforming well. It did get powder coated before installation as well.Screenshot_20200804-124120_Photos.jpg

Thanks!
 
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Usually better to get it signed off when it's still on a blueprint no?
I would have thought N brace the sides stern/transom bottom to engine mount top, not much need for the perpendicular brace from side to side near the stern JMO.. Too much stiffness can be worse than the right amount of flexibility in the right places in a design like that but I'm not an engineer and they are a fussy bunch knowing my son lol!
Early in my fabricating education an old fart looked at my work and told me it's going to crack here and here... he was right lol!
 
IMG_0668.JPG I hate bureaucracy so my builds are cheap and I just worry about public liability. My airboat I just built it like the guys in Florida have done for years. About 800 lbs of 489 500 hp BBC engine, seat stand attached so say 1500 lbs sitting above the hull with passengers mounted on a 1" square tube rail fastened to the hull, two rear uprights were 2" .125" and the rest 1" tube. 7' diameter propeller with a 2.86/1 reduction. I bet the whirl effect was astronomical when I did spins but I'm not an engineer so I wouldn't know how to calculate that. I would rather have a $4000 outboard (like I said I'm frugal) fall off than have something break on this rig lol!
 
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Wild Bill said:
Usually better to get it signed off when it's still on a blueprint no?
I would have thought N brace the sides stern/transom bottom to engine mount top, not much need for the perpendicular brace from side to side near the stern JMO.. Too much stiffness can be worse than the right amount of flexibility in the right places in a design like that but I'm not an engineer and they are a fussy bunch knowing my son lol!
Early in my fabricating education an old fart looked at my work and told me it's going to crack here and here... he was right lol!
Click to expand...

Funny you should that. I spent 10 years in metal fab (then somehow became a sheet metal contractor), so yes we love to design and build things. He story with my bracket is I had an old "gill bracket" from the Boston whalers. One day, 10 days before our holiday, I was touching up the paint on my bracket when the metal appeared a little soft. Next thing u know my fingers are through the bracket. Uh oh. Good thing I know fabricators to make some up that can replicate this.........and heer we are today. I am usually a man of procedure and guidelines, in this case it probably wasn't the best approach but it has worked.

Hopefully I can swing this, but worst case scenario I have to get a new bracket for the outboard.
 
Well the worst thing is it's powdercoated now. Just tougher to clean that powder coat off to change things if need be.
 
Wild Bill said:
View attachment 55502 I hate bureaucracy so my builds are cheap and I just worry about public liability. My airboat I just built it like the guys in Florida have done for years. About 800 lbs of 489 500 hp BBC engine, seat stand attached so say 1500 lbs sitting above the hull with passengers mounted on a 1" square tube rail fastened to the hull, two rear uprights were 2" .125" and the rest 1" tube. 7' diameter propeller with a 2.86/1 reduction. I bet the whirl effect was astronomical when I did spins but I'm not an engineer so I wouldn't know how to calculate that. I would rather have a $4000 outboard (like I said I'm frugal) fall off than have something break on this rig lol!
Click to expand...

Thats a pretty crazy build with that kind of HP.
 
I like it, might have to Snyderfy it a bit! :)
 
That's an interesting bracket. The workmanship looks very very good in the picture.

Two things come to my mind:

1. the wall thickness of the tubing is unknown
2. the design is weak in the vertical direction, relatively speaking. You have very little triangulation so you are mostly relying on moment forces at the end connections of the main fore-aft members. You can address this by installing cross-braces similar to the horizontal braces you've got, or you can weld a plate on the outside (called a diaphragm). See my sketches here:

bracket w brace.jpg bracket w diaphragm.jpg
 
Pineapple Express said:
That's an interesting bracket. The workmanship looks very very good in the picture.

Two things come to my mind:

1. the wall thickness of the tubing is unknown
2. the design is weak in the vertical direction, relatively speaking. You have very little triangulation so you are mostly relying on moment forces at the end connections of the main fore-aft members. You can address this by installing cross-braces similar to the horizontal braces you've got, or you can weld a plate on the outside (called a diaphragm). See my sketches here:

View attachment 55578 View attachment 55579
Click to expand...

Thanks for the compliments on the workmanship. I do wish we did more cross supports on the sides rather than the gussets in the corners.
All the material is 6061 aluminum. All the tubing is 2.5"x2.5" x 1/4" wall. The transom mounts are 3/8" plate and the outboard mount is 1/2" plate. As per your sketches, the plates on the sides would make the most sense for an alteration.

Do you think I could get a rating somewhere? Or better off putting a new single pod on it? The reason why I didn't pod it in the first place was I was a little skeptical on the added floatation on the stern, more so in following sea conditions.




Thanks again for the input Pineapple!

Paul
 
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Here are couple pics of the inside of the boat and 1 of the outside. . The flat bar connects right to the stringers with 1/2" bolts. I was planning on bolting pieces of 1/4" wall angles to the flat bar to add stiffeness.

Screenshot_20200807-135853_Photos.jpg Screenshot_20200807-135922_Photos.jpg Screenshot_20200807-135853_Photos.jpg Screenshot_20200807-140203_Photos.jpg
 
Pineapple Express said:
That's an interesting bracket. The workmanship looks very very good in the picture.

Two things come to my mind:

1. the wall thickness of the tubing is unknown
2. the design is weak in the vertical direction, relatively speaking. You have very little triangulation so you are mostly relying on moment forces at the end connections of the main fore-aft members. You can address this by installing cross-braces similar to the horizontal braces you've got, or you can weld a plate on the outside (called a diaphragm). See my sketches here:

View attachment 55578 View attachment 55579
Click to expand...

I agree with this also just looking it from the engineering side of the things. If you put it through finite modelling on computer I agree these would be your weakest areas. I would go with that right picture.
 
salmonkiller01 said:
Never heard of a bracket with max hp, other than kicker brackets. What is you boat max hp?
Click to expand...
I've been trying to find that out. I can't find any markers or tags anywhere on boat for a hull rating. I found an original manual, but that still didn't have the info. So, I emailed bayliner directly to find out and waiting a response. But, I also know the transom was rebuilt at the time of the conversion. So that may make things tricky too.
 
Pineapple Express said:
Is your pod/bracket made by a company that produces pods/brackets? Or is is a custom-made unit?

I'm curious for insuring a vessel like @sasqman 's if a rated bracket is necessary?
Click to expand...
Good question. They've never asked how the outboard is mounted, just details on the motor itself. But my current motor does not carry alot of value right now so maybe that is why. Definitely something I should ask about though if I end up moving forward with a repower. Thx again
 
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