Boat support stands / trailer transfer

[abl1111]

What size boat do you have FR Frank ? 20 or 23' ? That's an important distinction.

You use (3) 2x6 glued and bolted together - I assume you place this w/ the 2x6' pieces in a vertical position, as opposed to flat ?

As for the lifting, I was thinking of doing this w/ (2) bottle jacks, each lifted a little at a time until the boat was off the trailer. Then slide the trailer out. Seems like it would work, do you agree ?

[ScottM]

What size boat do you have FR Frank ? 20 or 23' ? That's an important distinction.

Look at both his avatar and signature.

[Trey1096]

Let me preface this by saying that I’m a structural engineer.

In order to get the beam high enough, you’d have to stack the blocks pretty high. If the blocks you’re using are normal CMU, they wouldn’t have any problem supporting the axial load, however, the lateral force resisting capacity would be EXTREMELY low. After you got the boat picked up, it wouldn’t take much to push it over. This could be a puff of wind, an inadvertent nudge, or maybe just some eccentricity in how they were stacked.

I’m not sure how much weight you’d be lifting in the front, but by code, a SYP #2 6x6 beam with an unbraced 10’ span can’t support more than a 750lb concentrated load at midspan. Fr. Frank is correct in regards to the (3)2x6x10’ beam being able to support more load than the 6x6x10’ (I’m assuming he’s talking about loading the beam in the strong axis, or upright). The code allowable for a (3)2x6x10’ SYP #2 beam is a 1050lb concentrated load at midspan. (Disclaimer: These values are just for a comparison. A lot of other stuff can come into play so don’t go hang 750lbs off a 6x6 and then let your wife crawl around under it. Evaluate the whole system to make sure it’s safe. Allowables per IBC 06, NDS 05)

The chain setup IslandTrader used put a lot of load on the chain supporting the hoist. The greater the angle in the “v” above the hoist, the more the tension on the chain is multiplied. The load through the chain is:

Tension in Chain = Lifted Load/(2*cos(v/2))
Where v is the angle in the chain above the hoist.

In his pic it looks like the angle is about 170deg or so. If the bow of the boat weighs 500#, the tension load on the chain would be 2868lbs. I don’t think it would be hard to find a chain to take that much load, but you’d need to be sure it was anchored off pretty good at each end.

Shrimpin’s method looks pretty good. If the posts are buried deep enough, the dirt will support the posts laterally in both horizontal planes. The beam looks heavy enough to carry a pretty good load, and the steel straps will keep it centered on the posts. You couldn’t figure out the capacity with a lot more information (post embedment depth, soil type, post size & species, beam size and species), but it looks like a good idea.

I say all of this because I’ve seen a lot of people get hurt by focusing too much on 1. components and 2. vertical loads. Not only does each component have to be able to support the imposed loads, the whole system has to be assembled in a manner that will transfer and ultimately resist the vertical AND horizontal loads.

Dry stacking 8” or 12” CMU to 7’ high and then placing a 6x6 across it to pick up the bow of a boat is not safe in my opinion. Even if 100 people have done it and never had a hitch, there is an inherent instability in the system that will jump up and bite someone eventually. Don’t let it be you.

If you have any questions, I’ll be happy to help in any way I can.

Trey

[Islandtrader]

Very nice presentation. It really puts all factors into perspective.

Makes me think that my 2000# rated chain might of been a tad light.

[abl1111]

Thank you for that explanation - done very well.

Now the $1,000,000 question - what can I safely use as a beam, assuming I mount a "V" notched for the "V" of the hull, made out of a 4x4 ( to help w/ stability ) - to lift the front of my boat for this trailer swap ?

I was hoping to use cinder blocks for side support ( they hold houses up ), I think (2) high would do it ( so - (4) for each side of the bow for a total of (8) needed ) Then use (2) bottle jacks, to lift the beam and the boat ...

What should this beam be made of ?

Lastly, does anyone know, maybe from setting up a trailer what the bow weight is of a 23' Tsunami, Sceptre ? ( No 20' need answer... )

Thanks all.

[76Red18]

Trey is right about the blocks being weaker when placed on their flat face. Block are non-structural, they don't hold houses up; its the reinforced concrete that gets poured in the "cells" of the block combined with a perimeter concrete beam that makes the "structure". 2 block side by side with the cells vertical with the next coarse or layer turned 90* to the previous coarse is the best way to stack them. Placed on a flat, level, well compacted surface,preferably concrete, this method of stacking would be ok up to about 4'. Fr. Franks 2 x 6's would be the way to go. You could even use 4 2 x 8's for the safty factor. As far as my credentials go, I'm the one that has to build the "over engineered" structures that architects and engineers like Trey dream up. I know ya gotta to do it that way because of the c. y . a. factor.

[Fr. Frank]

NEVER, NEVER, NEVER use concrete blocks stacked on their faces, or flat surfaces. They' break more often than not.

To support my transom, I stack 8"x16" 16lb blocks three high on each side, stacked horizontally, with flat sides perpendicular to the ground.
I place them under the corners of the transom, with w/ an 18' long section of 2"x10" on top, and a 16" long 4"x4" on top of that, placed at the outer chine, so that 2" to 3" inches extends beyond the rear of the transom, and 1/2" extends beyond the hard-chine along the length.
This allows me to tilt the motor all the way down without hitting the ground.

I NEVER crawl or work under a boat I have not tried to push off the blocks by hand. No Kidding!! I will put both hands against a hull and push and pull violently to make sure it is stable and secure, and even then I am reluctant.

After blocking a boat off of a trailer, I push hull supports in from the sides that look like this: They're made out of 2"x8" boards. This prevents the boat from rocking, and makes it safe to climb aboard and work.