Moving the chainplates to the Hull sides?

AtlanticAl · Feb 25, 2012

I had toyed with that idea, as my boat dosent have proper chain plates, it has flat plates under the deck, onto which a right angle plate goes up through the deck, and the rigging attaches to this. I think it would be possible to put them onto the outside of the hull, but, i think their would need to be some form of re-enforcing, on the inside of the hull, like a strip of plywood, glassed in, because with how thin the fiberglass is on the hull, i dont think it would take long, for the bolts holding the chain plates, to elongate the holes, and then leaks. I decided not to do it, because of the chance of it leaking, and having to constantly be re sealed. But i would have to do it, to find out if that was really going to be the case.

Benny17441 · Feb 25, 2012

I consider chainplates that attach to the outside of the hull to provide greater integrity and strength to the rig and are highly desirable in a sea going vessel. The benefit of not having them obstruct the deck area are a secondary benefit.

Ed Schenck · Feb 26, 2012

Why Benny? Because the chainplates are stronger? Or does the increased angle of the shrouds strengthen the rig? Maybe one of our engineer members can do that math. If you move a shroud out six inches how does that change the loads? Use my boat: mast = 52.5' from keel, 45' from the partner; four lower shrouds = 23.3'; two uppers = 43.7'. Remember too that you have to change the angle of the spreader brackets.

Jackdaw · Feb 26, 2012

Ed Schenck said:
Why Benny? Because the chainplates are stronger? Or does the increased angle of the shrouds strengthen the rig? Maybe one of our engineer members can do that math. If you move a shroud out six inches how does that change the loads? Use my boat: mast = 52.5' from keel, 45' from the partner; four lower shrouds = 23.3'; two uppers = 43.7'. Remember too that you have to change the angle of the spreader brackets.

Longer spreaders too. They have to end directly above the chain plates.

Remember it will probably require a switch to a non-overlapping headsail, no bigger than perhaps a 107%

Mathurin · Feb 29, 2012

We've had to go around them every day for close to 10 months and I can say that you get used to them very quickly, so I would suggest taking some time before investing to much time and money in such a project.

From a structural point of view, as said before, you'll need longer spreaders so that the lower section of the stays remain as parallel to the mast as possible. The spreaders may need to be beefed up to avoid buckling (this needs to be verified, as the section may already be overdesigned, as the rest of the boat). As for hull reinforcement, it would need to be investigated more deeply (hull thickness, lay direction...), but as always, if in doubt, and if it doesn't add a lot of weight/inconveniences, add material until you feel it's overdesign.

DianaOfBurlington · Mar 2, 2012

By moving the shrouds outboard, you limit your headsail sheeting options. Also, you will have the breach of hull integrity by fastening them to the hull. We built the first Cherubini 44 cutter for Warren Luhrs who wanted the chainplates bolted through the hull (probably for the reasons mentioned here). We never did get the combination of filler, fairing compound and gelcoat colors to cooperate. This is not a project I would take on willingly for anything less than a very major performance or safety gain.

The Hunters having the aluminum toerail were all built with a pretty hefty hull-to-deck flange. This method of assembling fiberglass boats has no equal (and the only thing better would be molding the whole boat in one mold at once, which is just about impossible). This hull flange is phenomenally strong, being a three-dimensional girder held in dimensional stability by the mere fact of its being there and having the deck fastened to it. This is why the stock boats' chainplates are fastened to or through the flange and the toerail. From a structural or performance perspective, I cannot think of anything better, especially since, if your boat has this arrangement, you already have it, so you don't have to do any work to get it.

Read Ferenc Mate's article on the C44 in the original Best Boats to Build or Buy to see the arguments my dad and others have used for the flange being the mounting point for rigging.

Also... my arguments for using u-bolts as chainplates have been stated in many other posts here. After my experiences with both, I would not willingly change to a bar-stock stainless-steel chainplate for the world. (The C44, arguably one of the most robustly-built boats ever produced, uses $12.99 Attwood ski-boat u-bolts for chainplates. Never a failure-- not one.

And-- and on a lighter note-- you do not know about hassle moving forward of the coaming under sail till you have sailed a first-generation Hunter 25!

DianaOfBurlington · Mar 5, 2012

I appreciate your faith in me, Pilot!

Of course there is nothing wrong or difficult about moving them to the toerail. As I may have stated many times I am fond of u-bolts and found the 1/4" ones at West Marine (SKU 599217) to be ideal for my H25. The factory provided a bent angle of stainless with three holes in it. I will remove this and install the u-bolts. It will mean less contact between SS and aluminum-- and so less corrosion of the toerail-- and more ease of maintenance and replacement if necessary in future.

You would probably need longer spreaders (on the H25 they are already made for this width) but this is not a tragedy. See DAMCo (Dwyer Aluminum Mast Co) for very nice replacements, any length you want. For your boat use true-5/16" U-bolts, simply removing one toerail bolt, drilling another, and fitting them with locknuts and a significant (long, with multiple holes) backing plate. In this way you gain the following:

-- Wider stance for your shrouds, room to walk by inside them;
-- Avoidance of hull holes;
-- The advantage of using the toerail as a backing block-- hardly likely you will bend that thing, let alone yank it off the boat;
-- Avoidance of maintenance of through-deck chainplates and the plywood they are attached to;
-- Use of very cheap, reliable, and easily-replaced materials (rather than very expensive chainplates now necessarily custom-made);
-- Use of proven design and engineering-- you are not breaking new ground here, only doing what has been done so often before;
-- Retained ability to sheet headsails inside the lifelines-- unless your stanchions are those freaky early-80s one that mount on the toerail and turn IN (why, oh why?).

Your boat does have a nice side deck and it is a nuisance to have to do the limbo just to move forward.

DianaOfBurlington · Mar 6, 2012

I would move the upper alone without the lowers rather than the reverse. The upper benefits from the wider stance more than do the lowers.

I am with you, Pilot, and find my best solutions occur after taking the time to contemplate each issue. Rarely do I get a purely-new 'Eureka' moment (though I had one today. I will post it to the blog when I finish what I started).

Are you really in Lucaya? --or, where is the boat? I would consider having a look at it for you.

H30Gary · Mar 7, 2012

Gosh, after reading this I'm really going to have to consider moving the shrouds on my H30 to the toe rail. Having the deck clear to go forward would be really nice. The jib (150%) on my boat sheets outside the lifelines so there would not be any performance penalty. I'm going to have to replace the standing rigging on my boat soon anyway (the turnbuckles have run out of adjustment room) so that might be the time.

AtlanticAl · Mar 8, 2012

I dont think you would need to change the spreaders, beacuase if you look up to your spreaders, the rigging goes straight up, it then curves at the spreaders, and goes to the masthead, if you moved it a few inches at the bottom, it would make no difference, i looked at mine, and its one side of the toe rail, as oppesed to the other side, it would make no difference to where the spreaders are.

You have to remember this is not precission engineering, they invented all this years ago, where ropes and lines were all aproximate, and everything was expiremental. Nothing is exact on a sail boat, you can move lines and stays a few inches, with no effect, i am thinking of moving my main sheet, five feet forwards of where it is just now, and i know it will work better there, it will just get in the way more.

DianaOfBurlington · Mar 9, 2012

Pilot, e-mail directly and know that I will definitely consider that trip! I'd be happy to look over the boat at any time if I can sort out how and when to get down there.

DianaOfBurlington · Mar 9, 2012

AtlanticAl said:
I dont think you would need to change the spreaders, beacuase if you look up to your spreaders, the rigging goes straight up, it then curves at the spreaders, and goes to the masthead, if you moved it a few inches at the bottom, it would make no difference, i looked at mine, and its one side of the toe rail, as oppesed to the other side, it would make no difference to where the spreaders are.

You have to remember this is not precission engineering, they invented all this years ago, where ropes and lines were all aproximate, and everything was expiremental. Nothing is exact on a sail boat, you can move lines and stays a few inches, with no effect, i am thinking of moving my main sheet, five feet forwards of where it is just now, and i know it will work better there, it will just get in the way more.

Al, you'd be surprised what a few inches either way does. For example, on an H30 you'd be moving them from the side deck to the rail about 8-12 inches outboard. This will account for the shrouds being about 2 inches too short. I would assume one would make new shrouds at this major change anyway; otherwise one will need to add toggles.

The goal of narrower shroud bases is to facilitate closer sheeting angles for headsails. This issue is therefore one of performance versus convenience, a compromise that prevails on every production cruising-class sailboat. Like my dad who designed these boats, I think sailing is about sailing, not barbecuing and doing laundry and lolling about in air-conditioned splendor, and so I prefer to err on the performance side. I am long used to what most people consider inconveniences afloat and consider them part of the sport of it all.

I know my opinion is not that of many people, of course. But I would try to discourage anyone from making design and engineering decisions without being fully informed; and so that is why I contribute to these bulletin boards. My goal is to teach others some realities that come from my own rare and rather specific experience and education and about which others might not get a chance to learn otherwise.

You comment about a wider shroud base not making a difference is, in point of fact, not wholly accurate. It is true that for most yachties, the effects of such a change won't be very obvious. That says more about the yachties, however, than it does about the engineering change. By moving chainplates outboard, the one thing that will be true is that you will not point as closely. Someone with an equivalent boat, not so modified, will definitely out-point you. He may also have more trouble getting around the rigging on his way forward.

As yacht owners and users we all have to make up our minds between what we would like for performance and what we would like for convenience; and I've already stated my view on that. Others will certainly have other views, perhaps opposite to mine. I would only adjure you, please, don't claim that yacht design of the 1970s was all 'experimental' or anything but about as high-tech as anything could have been. My dad, who designed the whole Hunter range till 1982, was an aeronautical engineer with a lifetime's worth of flying and sailing experience. To say he was only guestimating where to put shroud-attachment points and so on is to pay him an insult, not a compliment which he deserves.

To your boat, I will inform you with the very best of intentions that moving the mainsheet 5 feet forward on a 28-foot boat is going to more than double the amount of mechanical advantage you will need over that of your existing mainsheet tackle. It will reduce your sail control (the tail of the boom will fall off to leeward, negating 'twist') and impose potentially dangerous loads on the middle of the boom (where all breaks in booms happen, because of stress applied here).

Yes, midboom sheeting is very popular; and I dislike it from a performance and engineering standpoint every time. It is merely a compromise imposed on boat buyers by the marketers for the sake of convenience-- all facts will support this. Midboom sheeting, on the average production yacht (Beneteau, Catalina, Hunter, et al) is definitely not a performance asset. Whether or not you would prefer it for your own boat, I respectfully advise you to know beforehand what the realities about it are, and then make your choice from a position of being informed.

I hope you take this in the spirit intended.

AtlanticAl · Mar 10, 2012

I didnt say anthing about the 1970s, i was thinking more of the 1700s, when it was all expiremental, i think it still all experimental, and if you look at suhaili which was robin knox jonstones boat, it was built in india, by people who learned boat building from their fathers, and when they built it, they didnt know that it would be the first boat to sail non stop around the world, in the early photos, it dosent even have any spreaders, it was just built with basic tools, by indians who knew no maths or science, just basic boat building, yet that boat sailed round the world.

I have also seen photos of my own boat, with the main sheet much further forward, right now, its five feet aft of the boom, but out of the way of everything, i want to move it forward, it would still be connected to the same place in the boom, but would just be directely below the place on the boom its connected to, it would just make the cockpit more clutered, and make the boat more awkward, if their is more than just me aboard, but i think for just me, it will make the whole rig easier to handle, as their will be less rope to heave in, and everything will be closer to hand.

Jim Legere · Mar 10, 2012

DianaOfBurlington said:
Yes, midboom sheeting is very popular; and I dislike it from a performance and engineering standpoint every time. It is merely a compromise imposed on boat buyers by the marketers for the sake of convenience-- all facts will support this. Midboom sheeting, on the average production yacht (Beneteau, Catalina, Hunter, et al) is definitely not a performance asset. Whether or not you would prefer it for your own boat, I respectfully advise you to know beforehand what the realities about it are, and then make your choice from a position of being informed.

I hope you take this in the spirit intended.

Boy, its not often that I disagree with JC II! But I have to differ on mid-boom sheeting. As Wallace Ross points out in his encyclopaedic work "Sail Power", a mid-ship traveller, due to its geometry, exerts better mainsail shape and power control over a much greater range than a boom-end sheet and traveller. It also makes available mainsail draft control through boom bend. While the loads are greater on the mainsheet and the boom, engineering appropriate extra purchase, spreading the load over several boom bails, etc. can easily address these loads. My previous boat had boom-end sheeting, my 1983 H37 cutter has mid boom sheeting. There is no doubt in my mind that I prefer the convenience of mid-boom sheeting and I also believe it is safer to have the sheets out of the cockpit on a boat of this size and power.

Respectfully,
Jim

rardiH36 · Mar 10, 2012

I've been following this thread, but have refrained from entering ... mainly because I didn't get it.

We have one of the best sailboat designers of the time electing to place the shrouds/chainplate interface on each model where they are. And even today, boats are designed with a wide variation of chainplate placement. Why move them around unless one feels quite certain that a very noticeable improvement in performance will result? DianaofBurlington made this clear in his last post.

As for easier walking along the deck, will moving the chainplates out really be than much of an improvement to compensate for the many hours and many $'s of expense. And to compensate for the violation of the original design? On my 1980 H36, yes I could move the shrouds out to the toe rail -- maybe 6-8". And yes that would allow more foot room on the deck. But still the angle of shrouds would require that the head/torso be bent inward anyway to pass by. No matter what, the deck will never be a jogging track.

The only valid considerations should be will better performance and/or strength result? I've pondered many times the pros and cons of moving my shrouds inboard closer to the cabin top interface. For the reason DianaofBirlington cited. Less sheeting angle probably would allow better pointing. But moving the shrouds inboard would require real thought about how to insure strength integrity. Then one also also has to buy and install an inside jib track on the main deck next to the cabin top. Up to now, I sometimes use a reverse barber-hauler to pull the jib clew more to the center. This does pull the clew towards the center by up to a foot depending on wind velocity and the fore/aft location of the jib sheet snap blocks on the toe rail. But really I can't say for sure that I do much better on a close haul.

My other tighter sheeting thought is to limit my jib size to say 95% so that I could lead the sheets inside the shrouds when close hauled. The smaller jib size would prevent the leach from rubbing up against and under the spreaders which was an issue when I experimented with my 135 Genoa (even furled a bit). When off the wind, the jib sheet would instead be led outside the shrouds for sheeting on the toe rails as John Cherubini designed.

The attached pictures show the shroud into deck location on the 1980 Cherubini Hunter 36. Solid thick pieces of SS bar go through the deck and are very robustly tabbed to the hull. Its one very tough design.

Moving the chainplates to the Hull sides?

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