Bobsled Question

[Michael Colby]

I’ve got a big bobsleigh (seats 12) that was built to go on my logging bobs (2 sets of runners with bunks and attached with cross chains). Last year we bolted the sleigh body to the four metal strakes (the bars that would hold the logs on the bobs) that come up about 12 inches on the sleigh body’s sides.

The problem is that the whole thing felt really stiff and I’m wondering if bolting it on all four sides might be the problem. Would it be better to attach the sleigh body from the floor to the bunks (versus all four sides)?

I look forward to your thoughts.

[mitchmaine]

michael. do your sleds have bolsters? they are another set of bunks that pin to the center of the sled bunks and swivel and roll as the sleds move over uneven ground. your body should mount on them. hard for me to tell from your question if you were including them.
mitch

[Michael Colby]

Yes, I’ve got the bolsters pinned to the bunks. The four metal strakes come up from the bolsters and are bolted to the sides of the sleigh to keep in place. I’m wondering if it would be better to either not bolt it in all four places to give it some wiggle room or bolt/pin it to the bolsters — perhaps using the same type of pin that connects the bolsters and the bunk?

I’m going to try and attach the best photo I can fine (not very good). Hopefully you can see where I’ve bolted the body to the strakes.

[mitchmaine]

looks like you did it right. good idea. usually the bolster is made into the body of the sled, and it would seem that that would make it even stiffer. what is it doing that you don’t care for?

[near horse]

I’ve seen where the box sits on the bolsters w/ the pins outside the framework of the box – your box size might not allow this. Also, they had a block anchored to the bottom of the sled that would fit right in front of the front bolster and one behind the back one. If your bolsters are free to pivot then you should be alright IMO.

[Michael Colby]

It was built last year and just felt really stiff, like we had it bolted in too tight to take advantage of the bolster/bunk/two-runner scenario that should give it some give. I’m going to unbolt it on the two diagonals (front right/back left) to see if it give it some room to maneuver.

I’m also still curious to know if anyone has ever attached a body to the bolsters/bunks via the same pin that connects those two? To my very non-mechanical mind, it seems like that would allow the body to float more with the natural action of the two runners.

[chrisf.]

My rack is only held from moving forward and backwards with pieces in front of the front bunk and behind the rear. I have a small chain tied loosely from hooks on the rack to the end of the bunks that allow it to move somewhat independantly from the rest of the sleigh and keep the rack on if the sleigh upsets.

[mitchmaine]

michael, the pin in your bolster should have alot of play in it. it should be captured by the steel plate on the bottom of the bolster but be almost sloppy and be able to move easily. wonder if that is working against you?

[Michael Colby]

I think you’re onto something, Mitch. And there seems to be a connection with how the body is bolted and a lack of play in the bolster. I’m going to take it apart and reassemble it with those things in mind.

Thanks for the great feedback.

[LostFarmer]

Have blocks to keep from going forward and back then a couple of short chains to keep from going up. I have found with a sleigh that that almost worn out and sloppy is far better than too tight.

[Michael Colby]

LostFarmer: I’m having a hard time visualizing your last bit of advice. Would you, by any chance, have a photo? Because I think we’re nailing down the problem. Thanks again.

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