Ground tackle loads

[Stemar]

I want to build a small "bowsprit" to mount an anchor roller so I can store my anchor ready to deploy. I have an existing roller that I use for my swinging mooring chain and the anchor, which means I have the anchor underfoot when picking up the mooring, plus I'm not getting any younger and manhandling the anchor onto the roller in a swell is hard work!

What I need to know is the maximum load I can expect to try and pull the thing off. The boat's a Snapdragon 24 with 17m of chain plus octoplait. I doubt if I'll need to ride out any hurricanes - where I sail, if things get iffy I'll be able to wimp off to a marina!

I'm thinking of using 18mm marine ply in a U shape about 4" high and the channel a couple of inches wide to take a roller, glassed over where it'it likely to get clattered. It'll need to stick out about a foot from the front, so I reckon it'll need to come back over the bow around the same, possibly a bit more and be fitted to the deck with 10mm bolts throught the deck and a 18 mm ply backing plate. I've got a lump of mahogany I could use for the bottom as screws sideways into ply don't hold very well.

Does this sound
1. Overkill?
2. About right?
3. A bit feeble?
4. Forget it, you'll never come up with anything strong enough?

 

[captainslarty]

Sounds fine.. go for it

 

[vyv_cox]

I suspect that you may be asking a lot of a cantilever arrangement, if I am understanding you correctly, if the up-and-down loads become high, such as a fouled anchor or suchlike. I would be inclined to add a compression strut between the end of the bowsprit and somewhere down the stem of the boat. Stainless thick-walled tubing about 20 mm diameter should be fine.

 

[Searush]

Just a thought; would it be simpler & cheaper to just put a second bow roller alongside the existing one? I have two bow rollers, but still tend to lift the anchor back onto the deck & tie to the pulpit vertical support when "on passage" or entering harbour or picking up a mooring. The 35lb CQR only gets put on the roller when I actually plan to anchor.

 

[Stemar]

[ QUOTE ]
Just a thought; would it be simpler & cheaper to just put a second bow roller alongside the existing one? I have two bow rollers, but still tend to lift the anchor back onto the deck & tie to the pulpit vertical support when "on passage" or entering harbour or picking up a mooring. The 35lb CQR only gets put on the roller when I actually plan to anchor.

[/ QUOTE ]Certainly simpler and cheaper, but I want the anchor to live there all the time. Otherwise I mught just as well stick with the one roller.

Loads when retrieving the anchor will normally be limited to what I can put on the chain, 'cos I'm the windlass. If I have to motor the anchor out, and real brutality is required, I could move the rode to a fairlead and take a turn or 2 round the samson post.

Does anyone know what it would take to break a roller setup like I'm thinking about??

 

[santeana]

Is it practical to retain a roller on the bow to be used in extremis (e.g. fouled anchor)? Keep the overhang to the minimum to reduce bending moments. Sideways loads may be a bigger issue than vertical bending so again minimising o'hang would be a good thing. Maybe extend the base width of the 'U' and bolt through the "wings".

 

[Stemar]

The cantelever probably needs to be about a foot long to be sure the mooring chain can never foul the anchor. I'll be taking some measurements this weekend, then I'll have a better idea.

I've thought of having a wider base, but that would mean the joint between the horizontal part and the vertical parts which will give it stiffness would be in tension, which is a lot weaker.

 

[simonfraser]

west epoxy the plywood together
glass it over
protect the forward edge over which the chain/rope runs with a metal strip
sounds good to me

 

[roly_voya]

I think you will need the anchor to self stow, in which case a simple roller may not do the job. I would look at getting on of the double roller cantalever units and then mount it on a suitable chunk of wood to extend it over the bow. Will also stop any problems with chafe on glass. The loads will be reletively light as you have a good streachy rope to absorb snubbing which is about the only thing that puts a heavy vertical load on a roller. 18mm ply would probably be fine for the base or something like 11/2 Iroko might look better.

 

[FrancisRutter]

I had one of the cantilevered double rollers put onto my Fisher 25 and it was put onto a small bowsprit as you suggest. It has done the job.
The yard who did the work actually used a stainless steel plate which they covered with a piece of inch and a quarter teak, taken suitably back over the deck and with backing under the deck. Feels very solid.

 

[saltwater_gypsy]

In YM July07 they gave the following mooring loadings for a"typical" 30ft yacht
wind speed load
52knts 2000lb
64knts 3,500lb
100knts 5,000lb
130knts 6,000lbs

Plan ahead!!!!