Mast Stability while replacing chainplates

[chris95040]

Originally Posted by Blue Stocking

Same 50 year old stick. Had it out for overhaul and new standing and running rigging.

Ah gotcha.

I've got the same stick and I'm curious - is that 670 lb number a guesstimate or did you have some way to measure it?

I'm working out the details for a new aluminum mast and I've been wondering about trading weight for safety factor in stiffness (more safety factor resulting in more weight). The worst case aluminum stick is like 325 pounds though, so if this 600+pound figure is to be believed (and I've seen it a lot from sistership owners) then I think I can safely afford the additional weight aloft of this very stout aluminum mast and still come out way ahead of the game.

So naturally I've been trying to work out if these wooden masts really weigh 600 pounds or not. Taking the largest cross-section area of the mast and multiplying by its length, and the density of sitka spruce, the number I come up with after numerous attempts is well under 300 pounds. Sure there are other doodads and a few solid (non-hollow) spots along the length, but not enough to make up another 100% of the weight!! Even if it's actually fir as you suggest, which is slightly more dense.

[billdre]

I don't know if it's "his method" as such it's just what I know from his book, "Sailboat Hull and Deck Repair," plus he is a columnist for one of the sailing magazines and has other sailing maintenance books available. It means creating a solid epoxy core replacement and then cutting or drilling through it so the new hole is sealed off from the surrounding deck core. I'll look up the duplex stainless and other discussions you referenced. Thanks.

[billdre]

I appreciate the many suggestions and comments from the group. Really good ideas.
However, are there any other people who have actually left a mast up for a week or longer, on the hard, without the main shrouds to support it? Did it work out OK or not? One person had damage with no support. Any other experiences? Thanks.

[Stu Jackson]

Is this for your O'Day 28?

If so, doesn't DR (or DMR) Marine have O'Day parts? From what I've read about and from O'Day owners in other boating forums, the guys name is Rudy. If so, I don't understand the fabrication part of the question.

[GrahamHO]

Originally Posted by billdre

I've decided to replace my chainplates for next season. To be sure about receiving correctly made replacements I'm planning on sending the old ones to the firm that will make the new ones. So the question is ... has anyone left their keel stepped mast up with the upper and lower lateral shrouds removed for any length of time. Forward lower shrouds, plus fore stay and back stay would remain. Also I plan on using the jib and main halyards as lateral support anchored to stanchion bases. The stanchions are mounted on solid layup, no core, with back plates. Has anyone done this? For how long? Was it OK? Thanks.

Yes I did that a couple of years ago. My mast is deck stepped which might be considered more of a problem than keel stepped. In fact it was no problem at all.
I used the forestay which didn't need removing, plus the headsail halyard, the main halyard, and the gennaker halyard triangulated back to stanchion bases.
I also left in place forward lowers on their own chainplates that weren't being changed.


You will be fine using your back stay and main and headsail halyards with your fwd lowers in place. I did need to tie on more lengths of polyester braid to extend the halyards and I tensioned them back to stancheon bases with my version of the truckers hitch. That's a knot made into a purchase. I did make sure the halyards were very secure at the jammer ends also tying back to other cleats.


This was for maybe 2 months in winter weather as I did major interior work including removing the old chainplates and their knees, removing furniture and water tanks, fibre glassing, designing and constructing, and installing new chainplates, reconstructing the furniture to allow more room, and installing new flexible water tanks. Then finally repainting inside which I did the following winter.


Before you remove your rigging it's a good idea to put a couple of turns of masking tape around your rigging screws to mark the adjustment positions so that you have a starting point for setting up your rigging again. When you finally set it up put a sail slide in the main track and tie a tape measure on. Haul it up the mast on the halyard (with a safety down haul line) and measure down to your chain plates from each shroud / mast attachment point. Assuming your mast and chain plates are in the correct places they should measure the same on each side. Check that your plates are correctly positioned before you install them, with multiple measurements including back along each deck from the base of the forestay.


My mast is 40' above the deck. As yours is keel stepped it will be even more stable, though mine was perfectly stable.


It was a big job but well worthwhile. Removing the old stuff and the necessary sanding was the hardest and longest part.

[GrahamHO]

By the way; as above my boat was floating in its marina berth and exposed to some wave action from passing boats exceeding speed limits as well as to winter storms. No problems.

[GrahamHO]

Originally Posted by chris95040

Ah gotcha.

I've got the same stick and I'm curious - is that 670 lb number a guesstimate or did you have some way to measure it?

I'm working out the details for a new aluminum mast and I've been wondering about trading weight for safety factor in stiffness (more safety factor resulting in more weight). The worst case aluminum stick is like 325 pounds though, so if this 600+pound figure is to be believed (and I've seen it a lot from sistership owners) then I think I can safely afford the additional weight aloft of this very stout aluminum mast and still come out way ahead of the game.

So naturally I've been trying to work out if these wooden masts really weigh 600 pounds or not. Taking the largest cross-section area of the mast and multiplying by its length, and the density of sitka spruce, the number I come up with after numerous attempts is well under 300 pounds. Sure there are other doodads and a few solid (non-hollow) spots along the length, but not enough to make up another 100% of the weight!! Even if it's actually fir as you suggest, which is slightly more dense.

I couldn't quite work out if you are replacing a heavy mast with one 300 lbs lighter. Assuming that is what you are doing and that the COG of your mast is at say 5 times the length of the COG of your keel each measured from the water line; that will result in a stability increase similar to adding 1500 lbs to the middle ( COG) of your keel without the weight penalty.


Conversely if you are increasing the mast weight by 300 lbs; that will be a stability decrease similar to removing 1500 lbs.


In other words to maintain existing stability you should add 1500 lbs to your keel if you increase the mast weight by 300 lbs.


You can do exact calculations yourself working out the moments involved; but mine are reasonably close.

[billdre]

GrahamHO thanks so much for contributing with all the detail. I was hoping someone who had done this would chime in. Your project was much bigger and entailed more time. I will probably only have the shrouds down for 3 to 4 weeks.
Stu Jackson is right D&R Marine is a big O'Day supplier but according to their product lists they don't have chainplates for the 28 and they didn't respond to inquiries.

[GrahamHO]

Originally Posted by billdre

GrahamHO thanks so much for contributing with all the detail. I was hoping someone who had done this would chime in. Your project was much bigger and entailed more time. I will probably only have the shrouds down for 3 to 4 weeks.
Stu Jackson is right D&R Marine is a big O'Day supplier but according to their product lists they don't have chainplates for the 28 and they didn't respond to inquiries.

You shouldn't have any problems. Incidentally why do you need to replace your chainplates?

I replaced and completely redesigned mine. The originals were putting too much stress on too small an area of the hull. In New Zealand we traditionally don't have many production boats where like cars you can order a part for say a 1997 model. That's changing with imported boats arriving.

I made mine out of 316 SS which cost $600 for the materials alone. I won't go into the design as its not relevant except that I spread the load over a larger area and added interior glass and new knees to that part of the hull. The old plates lasted +30 years. With the new plates I can increase the rig tension and we sail to windward even better than before.

[mike d.]

Hi billdre I did mine just like that in 06. I have Gulfstar 37 in Newburyport. I got my 316 s.s. for a local fab shop. I did all the work myself with a vise, chisel, grinder, and drill press. I bent the angles with a hydraulic press, then polished them. It took me a couple of weeks, start to finish.

[koolekat]

left both masts unsupported for 7 months no problems, use your halyards to support

[billdre]

GrahamHO 5 years ago I rebedded my chainplates and there was some surface rust and a few pits on the plates where they pass through the deck. A month ago I noticed that water was once again seeping around the plates into the cabin, so I know the plates are getting wet where they shouldn't. So it's time. After 37 years I think it's reasonable maintenance.

[chris95040]

Originally Posted by GrahamHO

I couldn't quite work out if you are replacing a heavy mast with one 300 lbs lighter. Assuming that is what you are doing and that the COG of your mast is at say 5 times...

I'm just trying to verify the weight of my current mast in order to make those sorts of comparisons, Bluestocking and I have the same rig. Probably should have pm'd instead of spamming the thread.

[sailcrazy]

FWIW....We replaced the chainplates on our 1989 Taswell 43 during a major refit in 2011. We used 316S/S, then had them highly polished before we installed them. Most importantly, on the advise of several other yatchies and the rigger, we rasped/filed the deck back to almost a 45 degree angle on all 4 sides of each chainplate opening before we reinstalled the chainplates. Once they were bolted in and tightened, we filled the (filed away) space with sealant. The new, larger opening allowed for a tapered, generous amount of sealant, with lots of room to move without breaking the seal, around each chainplate. Then we restepped the mast and reattached the new rigging. And we haven't had a chainplate leak since!!!

[mitiempo]

Originally Posted by billdre

I don't know if it's "his method" as such it's just what I know from his book, "Sailboat Hull and Deck Repair," plus he is a columnist for one of the sailing magazines and has other sailing maintenance books available. It means creating a solid epoxy core replacement and then cutting or drilling through it so the new hole is sealed off from the surrounding deck core. I'll look up the duplex stainless and other discussions you referenced. Thanks.

An easier way is to use the new chainplate - or the older if they are the same size - as a former and place the thickened epoxy around it. Either wax or tape the chainplate first and removal after the epoxy sets - 5 or 6 hours - is easy.

I agree with Graham. Currently my deck stepped mast is held up with a halyard in place of the forestay and the uppers and lowers are both going to the toerail - snug but not tensioned really. I am replacing my chainplates which both uppers and single lowers are attached to and installing a custom bow roller that incorporates the forestay fitting.I am in the water.