Chainplates job and hull strengthening

[Julien de Tilly]

Hi everyone,

It's my first thread on this forum, but I have always find very good information in the past about many topics. So I am sure I will have good advices here. I need to replace the chainplates on my Hughes 29 this season. This how I conceive the project. Please feel free to let me know what you think about it.

First, the principal points I should keep in mind should be this:

1- To allow easy inspection and to avoid corrosion problem, the chainplates themselves should not be covered by fibreglass;
2- To minimize the stress on the chainplates and on the boat, the chainplates should be aligned with their respective shrouds;
3- To avoid exaggerated stress on hull, I should prefer an installation using mounting knees that needs to be glassed on the hull

This how I am now conceiving it:

1- Remove my current installation;
2- Strengthen the hull by adding layers of glass from the inside (and probably also from the outside, to fill the depressions that have been made by the chainplates);
3- On that thickened hull, glassed in wooden knees correctly shaped to sit against the side of the hull and the deck and to give the correct angle to the chainplates and their shrouds (but with no chainplates on them);

Question #1: Do you have any suggestion concerning the type of wood I should use? The backing blocks I've for my current installation (shown on above pictures were made of IPE. I was planning to use the same type of wood, for is resistance to rot and density, even though it would be hard to shape.

3.1- To prevent risk of rot, I will first apply a coat of epoxy on the wooden blocks.

Question #2: What do you think of penetrating epoxy? According to West System website, it doesn't seem to be a good idea, especially if I am using high density wood. (WEST SYSTEM - Projects - Thinning WEST SYSTEM epoxy)

3.2- To also prevent risk of rot, I was thinking that it could no be a bad idea to first drill larger hole for mounting bolts, fill them with epoxy, and re-drill them the correct size.

Question #3: Do you think it is a good idea and, if yes, do you have any suggestion concerning the type of epoxy I should use (pure, with additives and which one?)

4- Flatten the "front side" of the glassed-in wooden knees so as the chainplates perfectly sit on them.

Question #4: Do you think it will work or should I better try to have the chainplate seats already molded in the last layers of laminate when I will be glassing in the wooden blocks?

5- Drill mounting holes for chainplates and their backing plates through the glassed-in wooden blocks and through the hull.

Remark #1: I wasn't sure if outside backing plates were still a good idea, because I was fearing that stress apply from the outside on a relatively small areas (the ones covered by the backing plates) will generate again the same problem (I have considered for a period to do something more like what can be found under "Option 2" there : Replacing The Chainplates | SEA SPRITE ASSOCIATION). But the way I figure it now is that having the wooden knees glued against the hull with epoxy and glassed in will made the whole "one block" that should work together (i.e. the load apply from the chainplate to its backing plate will be distributed to a larger part of the hull, because the backing plate will pull the whole glassed-in knee "through" the hull.)

Remark #2: What decided me to have outside backing plates is that it seems to me the only way to easily remove the mounting bolts to inspect them and change them if necessary.

Question #5: How many mounting bolts do you think I need (is there a formula to calculate this?) and is their a specific pattern to place them (vertically aligned, "Z shaped" pattern, etc?)

Question # 6: Do you have any comments concerning Remark #2 ?

Question # 7: One problems that I see with this is that having the chainplates aligned with their respective shrouds and the outside backing plate sitting against the hull will create a problem with the angle of the mounting bolts (they will not rest at perpendicular angle with the metal piece on one of their side, which, I assume, will tend to bend them). Should I be concerned with that (especially with the lower-shrouds)? To avoid that problem, I have imagined that I could use thicker chainplates and ask the shop to drill-in mounting holes that will be parallel with the hull axis. What do you think of that ?

6- Install chainplates and their backing plates with the mounting bolts, sealing them with appropriate sealant.

Question # 8: Do you have suggestion concerning the material the chainplates, backing plates and mounting bolts should be made of? I've read that 316 stainless steel should be OK.

What do you think of this project ? Am I doing it the right way ? If you have any suggestions of comments concerning the whole project or concerning specifically asked questions, I will be glad to read them.

Thanks in advance to everybody.

[Reefmagnet]

Personally, I'm a big fan of just replicate / fix what is already there, assuming of course your boat is of a certain age and that the existing setup has seen satisfactory service. Simpler and you have less chance of screwing things up by overthinking.

[captjcook]

Welcome aboard!

Unfortunately, I am not seeing any sketches or pictures...

Calculations and designs of this nature are best left to a Naval Architect as loss of life or vessel comes into question.

So, for a theoretical discussion:

Are you wishing internal (through the deck) or external chainplates strapped to topsides?

If I were to make knees, I would make a quick basic shape mold box, line with poly sheet and build up knee with epoxy and biaxial cloth or roven if it was thick. Finalize shape with grinder and epoxy in using standard practices. Why use wood?

Hard to go further...

Chainplate attachment: Northstar 1500/ Hughes 35



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[GordMay]

Greetings and welcome aboard the CF, Julien.

[Scout 30]

There's a new round chainplate design that we saw at the St Pete Boat Show a couple of years ago. Supposedly a stronger design.
CSY Sailboats: Then and Now: Chain Plates/ CSY and for other Great Cruising boats worth upgrading: part 2

[reed1v]

Just replace with the same installation the boat came with. Your boat is designed a certain way and the stresses chainplates place on the boat are designed into the configuration. So unless you are a naval architect, leave alone.

[SVTwilight]

Originally Posted by Reefmagnet

Personally, I'm a big fan of just replicate / fix what is already there, assuming of course your boat is of a certain age and that the existing setup has seen satisfactory service. Simpler and you have less chance of screwing things up by overthinking.

I second reefmagnet on that.

On my recent chainplate refit (11 total) I replaced all the bolts, washers, lock washers and nuts with same sizes. I also use anhydrous lanolin on the threads as I do for all threaded bolts on the boat. I used the old chainplates as templates for the new at hte metal shop. I bead blasted the existing backing plates and reused them. I did go up 1/8" in chainplate thickness for more strength over time. This meant I had to slightly enlarge the holes in the deck that they pass through. On the two exterior transom chainplates I placed them (carefully) onto the hull surface with at generous layer of sikkaflex to keep water from getting in behind, which had been a problem. Then, tightened them up and quickly cleaned off all the excess sikkaflex that squeezed out. Same with the Drogue chainplates on the aft quarters.

Make certain the new chainplates are nicely electro polished to provide better resistance to rusting and pitting, and of course the nice shine is very pretty!

It was a fun project and a great feeling to have new and know materials in those important components.

Good luck!

[kentobin]

i'm replacing my deck mounted chainplates to external hull. i also need to add some angled standoffs under the chainplates. it was recommended to me to get a g10 fiberglass sheet and fabricate them from that. then glass them to the hull and make sure they would never break free or move or i'd get a shearing action across the chainplate bolts.

i was planning on using wood and don't remember if he told me why he recommended g10 over wood. i whined about the price and he said i wouldn't have to use that much of it. he's been working on and surveying boats for over 30 years so i know if i think i know better than him i maybe putting myself at risk but you don't know either of us. :-)

still pondering if i should stick with stainless or spend more money and go to titanium. quite often trying to save some money ends up costing me so much more. :-(

[captjcook]

G10 is a fiberglass layup...basically, make your own layup...easy.
I have pics on my android phone of titanium chainplates...do not know how to transfer to iPad to post...not easy...
Titanium chainplates are in fab shop to be remade in 316L. Brought in by local rigger. The holes for Clevis pins are wallowed out by at least 1/2 pin diameter on a 5/8 hole, 3/4 thick...not the first set to be remade...


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[reed1v]

Originally Posted by kentobin

i'm replacing my deck mounted chainplates to external hull. i also need to add some angled standoffs under the chainplates. it was recommended to me to get a g10 fiberglass sheet and fabricate them from that. then glass them to the hull and make sure they would never break free or move or i'd get a shearing action across the chainplate bolts.

i was planning on using wood and don't remember if he told me why he recommended g10 over wood. i whined about the price and he said i wouldn't have to use that much of it. he's been working on and surveying boats for over 30 years so i know if i think i know better than him i maybe putting myself at risk but you don't know either of us. :-)

still pondering if i should stick with stainless or spend more money and go to titanium. quite often trying to save some money ends up costing me so much more. :-(

Since you seem to be somewhat new to this stuff here is advice based on decades of experience owning sailboats, owning a family shipyard, and having an engineering background. Silicone bronze or monel for chainplates. Tried and true. Probably way less expensive than titanium and can be repaired almost anywhere around the world. Not true with titanium.

[Rigdaddy]

Originally Posted by reed1v

Since you seem to be somewhat new to this stuff here is advice based on decades of experience owning sailboats, owning a family shipyard, and having an engineering background. Silicone bronze or monel for chainplates. Tried and true. Probably way less expensive than titanium and can be repaired almost anywhere around the world. Not true with titanium.

I've seen many monel/stainless chainplates; how common are silicone bronze chainplates? I don't recall having seen them. I'm curious because I will replace most of mine this year.

[reed1v]

Originally Posted by Rigdaddy

I've seen many monel/stainless chainplates; how common are silicone bronze chainplates? I don't recall having seen them. I'm curious because I will replace most of mine this year.

They are not that common because they are not shiny like stainless. They will last, like monel, almost forever. The advantage is they do not get stress cracks like stainless when compressed, do not react to salt nor lack of oxygen, and virtually free of crevice corrosion which is the bane of stainless. If I remember right, Robin Lee Graham's boat Dove was fitted with silicone bronze plates. We had our ws43 fitted with monel and our luders with bronze. Fairly easy metals to work with. But again, not shiny. The boat market is not driven by what is best but what sells, which tends to be designs that are not that seaworthy, like open transoms, stainless everything, super wide bodies and flat bottoms; but do cater to the dockside crowd of weekenders.

[denverd0n]

I'm with those who say that you should just repair/replace the original design, and not try to change it. The original designer would have made all of the necessary engineering calculations, and taken into account all of the expected stresses. Unless you are qualified to do the same (and, if you were, you wouldn't be asking these questions) you should accept that he knew what he was doing.

Good luck.

[captjcook]

+1 reed1v. The chainplates In the shop are not mine nor my recommendation...just a witness to titanium failure...


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[reed1v]

Originally Posted by captjcook

+1 reed1v. The chainplates In the shop are not mine nor my recommendation...just a witness to titanium failure...


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the goal is to have metals that do not work harden. The only ones i am familiar with are monel and silicone bronze. Never worked with titanium so have no advice about that. If i was to replace a rig nowadays would go the route of monel plates, galvanized plow steel rigging, and bronze turnbuckles. Gives a flexible rig that will not work harden, stress corrode, nor crevice rot.