retrofitting chainplates to clinker hull

[greenbayboats]

Hi there, I'm fitting a tabernacle to an old clinker 30ft workboat which used to have an unstayed mast with dipping lugsail. New cruising grounds (with bridges) and a coachroof mean a new mast and rig . . . .
so should I drill for chainplate bolts through the steamed oak ribs, which are about 1 1/3in X 1/2 in, or make a shaped backing piece to lay against the inside of the planking between the ribs? or should I do something else? Thanks, Pete

[sdowney717]

http://www.classicmarine.co.uk/Articles/back.htm

also for example here:

Generally, attachment to the bulkhead is accompanied by through-bolting the chainplates to the bulkhead. In most instances, these bolts pass through the chainplates, through the bulkhead and through a backing plate which is used to spread the compressive loads created by the tightening of the chainplate bolts. http://express27.org/articles/chainplates

I would avoid damaging the frame ribs.

[greenbayboats]

thanks....

[rbgarr]

Is there a bulkhead?

[Russ Manheimer]

Here are the chainplates on Sjogin. The oak block is jogged to match the planking.

http://farm4.static.flickr.com/3341/3215673074_79c24c00e1.jpg
Chainplates visible at upper right. The bolts pass through the laps.

[Canoeyawl]

Not to discourage but there is no simple answer to your question.

Chainplates and standing rigging introduce new stresses and your hull may or may not be up to it. If it was not designed for this then you will have to do some retrofitting to avoid damaging your hull. (Bulkhead, ringframe, sisterframes, deckbeams, compression post, etc.)
There is also the question of buckling forces on the mast. The original partners add considerable column strength in this area and you may need to add lowers, babystay or make the mast a larger diameter to compensate for the loss of the partner.


Will the shrouds lead aft or will you have a backstay or running backs?
Will you add a headstay?
Are the deckbeams/coachroof able to support the compression loads?
Is the planking fastened well enough to share the load?

[Russ Manheimer]

What type of hull are you starting with? The sail area? Just for off-wind assist? Pics please....

Russ

[greenbayboats]

Thanks Russ and Canoe. . . . . . . . . .I will try to upload a photo. she was built in the '60s as a lighthouse tender in the orkney islands off scotland, copper fastened 7/8" larch planking with sawn oak frames up to near the waterline and steamed ribs between and above. big strong deckbeams but only one bulkhead , too far aft to be of use for chainplates. The rig will definitely be "auxilliary", she has a big air-cooled Lister Diesel and a pair of 14foot oars (!), I have a nice old canvas gaffsail and storm jib from my trawler (another story) which gives me a sail area of about 220sq ft, quite enough for a gentle motorsail or pottering along. And yes, I will have running backstays.....
can't seem to do photo now, will try later