[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