Lower Mast Bearing

[andya]

Had slight problem today in that my lower mast bearing decided to fall to pieces, fortunately in light winds so no other damage was caused. I need to form a replacement, the current one was made from what appears to be Plywood which has simply rotted. I have seen suggestions before that a variety of plastic type materials can be used, does anybody have any advice.

Thanks Andy

[X]

Hi Andy,

Most people use sheet Nylon – who built the boat originally & can you describe what the step looks like?

tx
Terry

[andya]

Terry,

The boat is a skinner built in 1977, Bearing was ply with a 80mm diameter hole with the usual key arrangement, don’t have all dimensions with me but it has a total depth of 15mm, with a step about 12mm down from which seems to be designed to stop any side ways movement. The whole thing is then secured in place with two metal strip which are bolted in place, this part is sill solid.

I noticed that the hole for the mast is cut straight, would it be better to cut it at an angle to help with the mast rake?

[X]

Andy,

Sounds like a starightforward replacement – yes suggest you make the hole about 10 deg.

Here is a good link for the material. Nylon6 will prob do the job.

Terry

http://www.theplasticshop.co.uk/

[davecooper]

Hi Andy,
I’ve got some 12mm acetal that I usually use for mast bearings. Do you know the outside dimensions of the bearing? If it isn’t too big to swing on my piddly lathe I can make you a new one.
Dave

[andya]

Dave,

Did anyone tell you are wonderful. However I have got some Nylon sheet on the way to me, so going to have a go myself on the basis that if i don’t give it ago will never learn. Going to simply stick it under my bench drill with a 10 deg angle on it, just how easy is Nylon sheet to cut, got a couple of hole cutters so thought I might give it ago with those!!!

Was looking at the dimensions for the mast hole, on the old one it was 86mm I know I will need a bit of tolerance but is 8mm to much?

Of course should I make a total hash of it, I may well take you up on your offer.

Thanks

Andy

[davecooper]

Probably better than me, actually: I have to bolt it to a face plate and it’s very tough to rake it and keep it really rigidly attached, so I usually bolt it on straight and bore straight through. The rules give a max play in the mast bearings:

12.7 Use
Movement of the mast, either at deck or at heel point, shall not exceed 7mm.
(ii) There shall be a security device of adequate strength such that the mast will not
come out of the step when the boat is capsized.”

You should go for max fore and aft, minimum sideways, but it’s much better to get the fore and aft movement by allowing the bearing to move rather than having the mast move in the bearing, so I suggest you get the bearing as snug as you can, without getting any friction.
Dave

[andya]

Dave,

Agree that it seems to make more sense to allow play on the bearing that the mast itself. My lower bearing is adjustable and I am not happy with the chocks currently in place (to flimsy and suprisd they have not broken). My intention to to machine some replacements.

I can find lots of varied advice on the position of the mast in the deck bearing but nothing for the lower bearing, this info would be helpful as it would allow me to machine the chocks to size in order to ensure the mast position is correct.

Andy

[Author]

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