Stemhead roller

[Alexis]

Dear all,

I am currently refurbishing a 34 feet cutter.
It seems that chafe on stem heads for anchor chain/rode is a recurrent problem. I am thinking of having a different system than what is susually found on boats. As I have already wrote ("Windlass installed off-center", posted 30.07.03) I am going for a slightly unconventional installation. For this reason and to give a fair lead to the anchor chain/rode, I am considering installing some sort of swivel block, meant to take chain or rope, that would hang from a small SS structure that'll stick out from the bow. Idea is that whatever the angle (within say 70° off the centerline on each side) the chain would not touch anything else than the block. The block could be open, by way of one of its cheeks for example.

Any intelligent remarks are welcome,
Cheers, Alexis

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[vyv_cox]

Your small SS structure will need to be very strong. Anchor rode loads are extremely high, especially in significant seas. Putting the swivel further forward increases the leverage, so strength needs to be even higher.

Personally, I have never experienced significant chafe of the stemhead fittings, despite keeping boats on swinging moorings for many years. Are you sure you are not inventing a problem to solve?

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[Alexis]

Very good point.
I undrstand that the loads will be tremendeous.

Have you read my thread about unstalling my winlass off center ? What do you think of it ?

You may well be right, as far as inventing a problemto solve,thank you.

Cheers
Alexis

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[MainlySteam]

I also have not experienced any problems with a chain over a bow roller and agree that you may be creating a problem to solve. However, for your situation aft of the bow roller with the angled pull back to the offset windlass, there is a photograph on page 107 of the August 2003 Yachting Monthly in an article on a family of yachts designed by Greg Elliot here in New Zealand which shows, not very clearly, how it is done on them. It appears to be similar to a stem head roller on its side. In the boat in the title photograph of the same article there would seem not to be any special arrangement at all.

Elliot is a very well respected designer so one could assume the anchoring solution is good, but I would make the point that while these are intended as cruising boats they are very light vessels (the 50 footer is just 12.5 tonnes lightship of which nearly 4 tonnes is ballast, and the 41 footer 6.5 tonnes of which over 2 tonnes is ballast).

John



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[Mirelle]

Another approach

First, make the roller as big as you possibly can, 150mm diameter is not silly. It can be made of a tough plastic. Mine is.

Second, if instead of making it with a ( shaped groove, you make it with a LI shaped notch in the middle, it handles chain better. Honest. I was persuaded into this, and it is right.

Third, think about arranging a chain pawl as part of the system.

Fourth, be certain to include a positive closure such as a keep pin.

Now, looking at sideways loads, there are very few of these but one that does occur is when the boat is aground and being kedged off!

I have a nice big Lewmar snatch block shackled to a strong eye just inside the stem which handles these - this has proved itself in practice.

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[AndrewB]

I'd urge a little caution about the range of reasonable-sounding but slightly unconventional changes you are proposing for this yacht, during refurbishment for blue-water cruising.

I went down a similar route - and found myself later changing back nearly all the changes I'd made in the first flush of enthusiasm. The ones I didn't do from my original list now seem irrelevant. It wasn't until I'd been blue-water cruising for a while with the boat that the changes I started to make really worked in the long term.

There is a lot to be said for keeping everything really orthodox using very standard stock parts from mainstream manufacturers as this is by far the simplest for maintenance, specially when away from the major yachting centres.

On the other hand, admittedly it is fun to experiment.


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[AndrewJ]

as an additional point, a friend of mine had installed an "eye bolt" near the waterline on the bow. To this eye he would attached a snatch block which had a "spring line" which would attach via a hook to his anchor chain, the other end of the spring line he would, after running thru the block, attach to a cleat on his deck. This in effect reduced the scope of chain he would have to put out and also put the point of attachment lower on the boat, reduced the load on the anchor rollers etc and he swore that with this arrangement, he was able to ride at anchor with less overall movement of the boat. Of course the eyebolt arrangement through the bow had a backing plate on the inside.

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[vyv_cox]

Your second

I replaced my ( shaped roller with a LI shaped one simply by buying a Plastimo one. Not as large diameter as 150 mm, I would guess the larger diameter is about 70 mm and the lesser about 30 mm. Length was identical to the one originally fitted by Sadler, something like 100 mm. The groove handles the chain well, as you say, especially beneficial for my new power windlass, and is additionally a good seat for the narrow stock of a Delta anchor.

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[Mirelle]

I\'ve got that setup

or rather, a simpler version. Eye on stem at waterline has a 12mm nylon rope shackled to it. Outboard end of rope is rolling hitched to chain and chain veered until the load is on the rope.

Cribbed from a photo in Don Street's "The Ocean Sailing Yacht".

Of course, the rope looks a bit odd (but not as odd as a snatch block at the waterline) - having a sizeable bowsprit, I simply belay it on the lower bobstay block.

A very serious backing plate is indicated - mine is 8mm bronze, about 5" x 18" - it also backs the bobstay eye, of course, and. mine being a wooden boat, it and its associated bolts and another big lump of bronze on the outside of the stem hold the stem scarph together.

This system definitely works - if I could find a chain hook (I think I will finish by making one) that holds my chain reliably that would be better than the rolling hitch.

The snatch block set up would be better when you want to veer more chain - with my set up you need to get the hitch on deck first, undo it, veer more, then belay again.

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[Alexis]

I have checked Elliott's site and can vaguely see the set up he uses on his yachts, which indeed seems much simpler. All I have to do just give an angle to the bow roller. You have convinced me.

Many thanks,

Alexis

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[Alexis]

Re: Another approach

Imagine the size of the roler is important. Just one thing I didn't understand: could you develop your idea about the LI shaped notch in the middle please?

Will go for the big snatchblock solution

Many thanks, cheers
Alexis

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[Alexis]

Will take your remark into account, and forget about my block. I'll go for the of center windlass and standard roller, ligned-up with the windlass.

Thank you,
Alexis

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[Mirelle]

Re: Another approach

The big roller greatly reduces the friction in the system - it really does make a huge difference. Back in the days when Camper and Nicholson were making GRP boats between 30 and 40ft, they had big stainless bow rollers. Good idea.

Today's production boats are mostly built down to a price and they don't have these details.

Now, about the notch in the middle of the roller. Instead of making the surface of the roller concave, make it flat, but cut a notch with parallel sides and a flat bottom in the middle - the notch should fit one link of your chain.

What happens is that the chain "magically" arranges itself so that each alternate link is horizontal and the next one is vertical. The chain cannot twist, or rather any twists are automatically taken out by the roller before it gets to the windlass. The chain is also rather less likely to jump out of the roller.

I hope this makes sense!


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[PeterGibbs]

The part of your posting that concerns me is the "small.. swivel structure sticking out from the bow" The side stresses applied when the boat is at anchor and being blown about are considerable. Whilst the idea of some system to guide the anchor line is appreciated, there is every chance that anything less than a very solid extension is going to fail, even to the point of rendering it impossible to raise the gear. The evidence of this risk is demonstrated in your comment about previous wear.

I have seen arrangements with rubber rollers N.S.E &W of the stemhead fixture, that accommodate these stresses; but they are built deep into the stemhead to accommodate the lateral and vertical sheer.

PWG



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