Smooth daggerboards under load

[Ryan..]

I would like to build bearings for high aspect boards that'll take around a 5ton+ load, that will allow for very easy raising lowering under load.  Without the need for electric winches or hydraulics, if at all possible. 

Searching around for examples , finding mostly machined bearings from branded polymers, uhmwpe etc. but not finding any ball bearing or roller bearing style examples.

Anyone have experience on the pro's and con's of building in roller style bearings for trunks?

 

[hump101]

Roller bearings under load in a fixed position will either have flats or will divot the board, depending on which is softer, so if you want to use bearings you need to make sure they are not under load when in a fixed position.

Consequently, this requires a complex support that allows the bearings to move against the board when required. Prone to issues of fouling and corrosion when below the waterline.

Another downside is that the structure of the board must cope with the shear loads induced by the friction when moving under load, so better to create a system that can relieve the load as the board is moved. The best you could hope for would be about 1 tonnes vertical load to move a board with 5 tonnes on it, so a lot of force required.

I can't think of any pro's......

 

[Ryan..]

Roller bearings under load in a fixed position will either have flats or will divot the board, depending on which is softer, so if you want to use bearings you need to make sure they are not under load when in a fixed position.

Consequently, this requires a complex support that allows the bearings to move against the board when required. Prone to issues of fouling and corrosion when below the waterline.

Another downside is that the structure of the board must cope with the shear loads induced by the friction when moving under load, so better to create a system that can relieve the load as the board is moved. The best you could hope for would be about 1 tonnes vertical load to move a board with 5 tonnes on it, so a lot of force required.

I can't think of any pro's......

Thanks much Hump, sounds like it may be a dead-end 

 

[guerdon]

Time your hoists with your tacks, so that neutral load during luffing.

 

[MKF]

Impossible to move under load --- on the 11s if you didn't time the board movement during a tack/gybe it stayed down...broke many block trying to adjust under load.

Anything over 7knots and a bit of heel  was stuck where it was...getting down just as difficult - manual system - purchase 3:1 and harken 44 winch....

Just get the ballet right, adjust in the low speed low load maneuver's

 

[Kenny Dumas]

If you really want to do it right, maybe use a hydrostatic bearing. 

 

[Zonker]

Rolling shear failure is a thing.

Anyway the way I adjusted my daggerboards (40' catamaran, about 1.8-2m extended into the water / 600mm chord) was to just apply a bit of load by pulling the lifting rope vertically (2:1 purchase with a sheave embedded in the board).

It would sometimes take a few minutes but there would be often a split second when the board would unload and you'd yank it up 200-300mm at a time.

At speeds much above 8 knots it never would seem to get unloaded, so yeah, wait to tack or luff the boat.

 

[Zonker]

Or do what Cariboni do with their lift keel. Rectangular trunk; top of the keel is a rectangular box with slippery bearing pads. 

(This is sort of speculation looking at their online info). Green surfaces are sliding bearing pads. It uses locking pins from outside the trunk to lock the keel in down position)

yes, they use a hydraulic cylinder to raise/lower.

 

[Ryan..]

Or do what Cariboni do with their lift keel. Rectangular trunk; top of the keel is a rectangular box with slippery bearing pads. 

(This is sort of speculation looking at their online info). Green surfaces are sliding bearing pads. It uses locking pins from outside the trunk to lock the keel in down position)

yes, they use a hydraulic cylinder to raise/lower.

View attachment 476977

Interesting thanks for the lede

I was thinking about a rectangular header such as that, but with "skateboard wheel" type rollers on all 4 sides, a series of them on up.. trick is to make it serviceable though. hmm...

 

[Zonker]

Hard plastic bearing surfaces don't need servicing in any sense. Replace when worn.

Wheels with bearings do. And they don't like to be loaded in a static condition for long periods as mentioned above. 

Just take the hoist line to a winch. Easier solution because you don't actively trim daggerboards up/down very often.