Timber beam supporting boat during winter

[ajk1]

A friend stores his 3500± pound boat in his boat house at his cottage (summer home), by lifting the boat up after bringing it into the boathouse and inserting two wood beams, one near the front of the boat and the other near the back of the boat, and then lowering the boat onto the two beams. The beams are currently wood and he says the wood is rotting so he wants to replace the wood beams with steel beams, and he wants the beams to be as light as possible, because they have to be manhandled into place. I have not seen the boathouse. He says that the existing wood beams are "about" 9" square.

I would calculate the resisting moment of the new beams as though they are laterally unsupported for the full span. I think his concerns with wood rotting could be addressed by using pressure treated incised timber, then soaking the sawcut end of each timber in preservative, and as an added measure coat the entire surface with preservative even though the beam is pressure treated. Re-coat every few years.

My question is: would the timber beams eventually twist?

If so, then steel would be the better choice I think, although it would have to be protected from corrosion.

 

[ajk1]

To Canuck65: Thank you for that very helpful information. Yes I agree that he should order pressure treated wood. Then I would suggest that he should soak the sawn ends of the wood in the preservative himself. Then as added measure he could apply the preservative to the full length of the beam. Every few years ho should re-apply the preservative. That is what I did when I re-built the rotting deck of my house porch (from the previous owner) and it is now> 20 years old and no detectable rot. I am not so sure about the effectiveness of stain against rot, compared to wood preservative, although I suppose if it is periodically reapplied that would help. In summer when the beams are not required to support the boat, he should store the beams up on blocks so that they are not resting on a wet floor.

I have assumed in calculations to-date that 2/3 of the boat weight goes to one beam, 1/3 to the other beam and the boat weighs about 3500 pounds max.

To minimize the weight of the beam that has to be manhandled, he could cut it into 2 beams placed side-by-side. i.e. take the 191 x 241 No.2 D. Fir beam and cut it into 2 beams each 191/2 mm wide, placed side-by-side.

Yes #1 D. Fir would be the lightest weight option, which is what is wanted, but I was of the belief that #1 grade is not very available in Ontario. Have you found that it is?

 

[Canuck65]

You can easily source D.Fir No. 1 timbers in Ontario. Either rough sawn or dressed.