chainplate design

[redhead78]

Chainplates and design have and always will be a big topic for us with sailboats, as seen with recent posts, and looking at Ron,s Benny hull chainplate damage, I cannot even imagine how this would make me feel, especially on a new to me boat, good luck to you on your repairs. I never liked the way it seems chainplates have evolved, last year, after completly rebedding mine on deck, I see them as quite a pain in the ass, especially if you are going forward in a hurry, duuh, seems like I am always hung up on them..I was at one time considering moving them like 3 " over and having like, 1/4" thick, 2" wide by approx 18-20" ss straps thru bolted to the hull , with 5/4 Mahogany glued inside hull and SS backers. Look at pics this would really free up deck, I can do this myself for basically the price of 6 straps I would need fabbed. This is the design of the old school, and with my 1977 Jenneau hull I think would be stronger than any deck mount. Anyone see and pros/ cons ?? Red

 

[Jackdaw]

Red,

Chainplates thru-bolted to the hull is a time-honored way to attach shrouds. Also remember you will need new spreaders!

It will probably also mess up your ability to fly genoas; at least make it a hassle.

I would also have the work vetted by a marine architect... without this I'm sure your insurance company would not pay on a rig failure claim.

 

[alexco38]

Yep, mid deck or outboard shrouds are real pain especially outboard. From your picture I am not sure you can even fly the jib on a close haul with the sheet on the outside. You'll have to switch the sheet or move the track.

The Hunter 30ish model has a similar problem with the B&R rig. The chain plate is outboard on the toe rail. The jib sheet has to thread between two shrouds thus making a big jib not possible. When you go forward, you have to lean sideways inboard. I dropped my prescription $$$ glasses into the lake because of that.

I wouldn't touch it because there must be something underneath to spread the load. I can't believe it is just thru-bolted to the deck. Doesn't matter how thick it is. Horizontal deck is no match for vertical bulkhead or rods. There has to be some vertical member to spread the load to the bottom of the hull.

I agree with Jackdaw. Insurance company may not like you.

 

[redhead78]

I have a 150 Genny, the sheets are on the lifelines and stantion already, wheres the conflict?? My sail is beat up cause of it and I have to replace and soon, I had already decieded on a 135%, ...Red

 

[Jackdaw]

I have a 150 Genny, the sheets are on the lifelines and stantion already, wheres the conflict?? My sail is beat up cause of it and I have to replace and soon, I had already decieded on a 135%, ...Red

Well could be OK. It depends on how you sheet and run the sail. Inside the lifelines? There will not be much/any room there anymore between them and the shrouds. And your new longer spreaders will poke hard at the sail when close hauled.

 

[redhead78]

What I meant was I am already outside the lifelines and stantion with the sheet, and moving the chainplates over like 3" to the toe rail they will still be inside the lifelines.Your concern about the spreaders is something I will have to look into... Red

 

[Jackdaw]

Your concern about the spreaders is something I will have to look into... Red

Yea. For proper rig geometry the V1 shrouds (lower caps) must always be perfectly vertical. That's true on any sailboat. So if you move your plates out (and slightly back), new spreaders are in your future!

 

[RichH]

Your chainplate location at mid side deck seems to be an afterthought, except if one has a split personality to get past them.


The important thing in any redesign is that the angle of the jib/genny - from the tack to the 'normal' location of your jib fairlead cars - is at about 10-12° from the centerline.

For elegant and 'pure' mechanical design, You might want to take a real good look at the 'rod system' that the later Beneteaus are using instead of traditional flat chainplates. Plus, if the angle that the cap shroud makes with the mast top can be kept at ~10° (perhaps with the addition of an auxiliary spreader set, etc.) you can consider moving the through decks CLOSER to the coach roof ... if this is a possibility, you might want to contact the spar manufacturer to 'rerun' the flexure and strength calculations (for fee) to see if this is possible, as the entire 'system' of plates/spreaders and their geometry should be 'optimized' as a single 'structural system', and not a collection of 'components'. For offshore, you'd probably have to increase the base width ... moving the 'plates' towards the rail; but, for 'coastal' you'd probably want to get that cap shroud base 'narrower' ... its the intercept angles that the cap shrouds make with the top of the mast is what usually defines the possible geometry ... about 10°, so that the stress remains within/under design limits of the attachment points (about 25-30% of 'breaking strength') when the boat is 'heeled over' at about 45° under full load, etc. .... the spar manufacture will have all these strength values based on your specific mast section and cap shroud attachment hardware. Vertical capshrouds are just a design/style element, its the angle that the caps makes with the top of the mast which determines how many spreaders are required ... and do they 'match' the flex/strength characteristics of the 'system', they can be at at non vertical angles.

;-)

 

[robertsapp]

Caution is advised

With all due respect, this really isn't a "what do you guys think" sort of situation, like "where do I put my chartplotter display?" If you're an engineer with some experience in vector analysis and static and dynamic load calculations, and you've worked out all the relevant moments, angles and loads, you might be able to redesign your rig safely. But I can assure you that the person who originally designed your rig did exactly that sort of analysis, and the solution they came up with represented the best compromise of performance, reliability, and cost. Changing anything is a bit like moving load bearing walls around in a building. Not something that's generally recommended without the proper analysis. I'd advise caution.

The more I've learned about chainplates, the more I've come to admire Hunter's solution. Because the wide stance of the B&R rig naturally supports moving the chainplates to the edge of the boat, it makes for a very simple installation with no deck penetrations. The majority of the chain plate is actually the reinforced composite buildup on the hull interior, composed of multiple layers of oriented glass fabric which spreads the rig loads across the hull interior and down to the lower liner with its stout support beams. No hidden or internal bolts, tie rods or other metal components to corrode and fail. And because the design of the rig is based on using a full roach mainsail for the majority of the drive, there's no need to use a large jib, and so the sheeting angles can be kept very narrow, improving pointing ability. But yeah, you do have to duck under that lower shroud when moving forward. I've left a bit of scalp on mine on more than one occasion!