Mast Support Post

[richardbrennan]

You might recall I was asking for assistance to cure a mast panting problem on my Westerly Ocean 33. I will not bore you with the whole saga, but I found out from XW Rigging that Westerly/Selden unusually specified tensions for both the cap and lower shrouds for this particular rig and so had the rig set up accordingly. These tensions are high and have resulted in the stainless steel mast support post taking on a curve of its own which is clearly not a good thing! This too is a known problem on some of the earlier boats and later models had a beefed up post of noticeably thicker diameter.

I clearly need to replace the post with a beefed up version and know from another later O-33 that the outside diameter is nine centimeters. What I don't know is how thick the wall is as there are flat plates welded on top and bottom, the top one taking the bolts from the mast step through the deck and the bottom one resting on a heavily reinforced area of the hull. From what I can see on line, 2 mm seems to be a pretty standard wall thickness, does anybody know if thicker stainless tube is available and from where? I also need to know who might make up such a support in the Portsmouth/Gosport area, Madge Marine has been suggested?

 

[theoldsalt]

Might I suggest you also contact the Westerly Owners Association as they will have documented recommendations if this is a common problem.

 

[vyv_cox]

Pipe sizes are known as 'schedules'. See this chart http://www.crp.co.uk/technical.aspx?page=141 Note that the size quoted is the bore, so you are looking for 3 inch. What you have seems to be Sched.5 and all others are bigger. AFAIK stainless pipes come in the same schedules. Try a refinery/brewery/plant installation company for a small offcut.

 

[richardbrennan]

Old Salt

I am trying the WOA

Vyv

It certainly looks as though I am looking for 3 inch; what I don't know is the wall thickness. Would you have a view as to what would be pretty bullet proof, it's obviously under a lot of compression?

 

[TimBennet]

Go for a larger diameter if at all possible. Stiffness (the ability to resist buckling) goes up with the square of the diameter. A little increase makes a big difference.

 

[vyv_cox]

Old Salt

I am trying the WOA

Vyv

It certainly looks as though I am looking for 3 inch; what I don't know is the wall thickness. Would you have a view as to what would be pretty bullet proof, it's obviously under a lot of compression?

I think it may be a matter of what you can get. Going to Sched.10 only adds about 50% to what you have. 20 and 30 seem to be unlisted, whereas everybody lists Sched 40 and it is very common in oil installation pipework.

 

[30boat]

In my opinion a stainless tube is not the best for a mast support.Wood is better.It's very strong in compression and all Fulmars have their mast supports made of it .My Fulmar has a solid mahogany post and the rig is tensioned at 25% of the breaking load of the wire which is a lot .In 34 years there was never a problem.I've heard of several instances of stainless tubes buckling.They were obviously badly specified but still I'd prefer a nice wooden post.

 

[richardbrennan]

I had not thought about wood, I'll give it some consideration. What is the thickness of your post?

 

[rhumlady]

The Konsort has a 10cm square post but it is built around the main bulkhead with about 4cm in the main cabin and at the forward side. The heads door bulkhead also forms part of it. The whole lot is screwed together using large stainless screws. It is not glued up though.

 

[PabloPicasso]

In my opinion a stainless tube is not the best for a mast support.Wood is better.It's very strong in compression and all Fulmars have their mast supports made of it .My Fulmar has a solid mahogany post and the rig is tensioned at 25% of the breaking load of the wire which is a lot .In 34 years there was never a problem.I've heard of several instances of stainless tubes buckling.They were obviously badly specified but still I'd prefer a nice wooden post.

+1. Wood is strong, readily available and easy to work. I'd use wood.

 

[30boat]

I'll have to check it on the boat ,I'm hoping of going there Saturday evening.

 

[Concerto]

If you still want to go with the stainless steel support then contact Trafalgar Yacht Services http://www.westerly-yachts.co.uk/ as the owners both used to work for Westerly and have plenty of records. They could also supply the support if you wanted.

Personally I would go with a timber support as it is more tactile and better looking. I would guess on my Fulmar it is about 90 to 100mm square, but not being on the boat I casnnot confirm this.

If you are not a member of the Westerly Owners forum http://www.westerly-owners.co.uk/woaforum/ then you should join, its free. As an owner you should consider joining the association http://www.westerly-owners.co.uk/ it does not cost much. If you are going to the Southampton show, they usually have a stand to chat with some owners and to join in person.

 

[ripvan1]

I used a length of 4" x 4" steel box section then clad it in ply and put wood edging on corners - plenty strong for 13m yacht - you could scale it down I suppose. Or go for wood as suggested.

 

[alahol2]

Try Solent Welding & Fabrication http://www.solentwelding.com/marine.htm.
They may know and could certainly fabricate it. They supply some Westerly stainless parts.

 

[jerrytug]

A very interesting discussion for me as my Hurley has a similar problem, which other owners have cured in all sorts of ways, it's true that the fatter the support, the less it can buckle, but then it starts occupying real estate, right where you want clear access in to the fore cabin.
Any yacht which suffers this issue was designed wrongly..

 

[TQA]

I would add something to your existing support to stiffen it.

4 lengths 15 mm x 4 mm cross section welded at intervals and spaced at 90 degrees should do it.

 

[john_morris_uk]

A very interesting discussion for me as my Hurley has a similar problem, which other owners have cured in all sorts of ways, it's true that the fatter the support, the less it can buckle, but then it starts occupying real estate, right where you want clear access in to the fore cabin.
Any yacht which suffers this issue was designed wrongly..

An interesting comment as it's self evidently true yet leaves a couple of questions...

Mast compression post load is one of the easier calculations in yacht design. The force is at a maximum at the maximum righting moment from the ballast and form combined. The designer should know these figures and then it's a very simple equation involving the dimensions of the rig. Allow a safety factor of a multiple of several and you can specify the post. (The static load from the rigging tension is effectively irrelevant and a red herring for calculating the maximum load on the compression post.)

As someone else has pointed out, the stiffness of the tube increases with the square of the diameter so intruding into living space shouldn't be a problem.

I'm very surprised that the original designer would get the spec wrong. Perhaps there was an unauthorised compromise made in the build for a few boats.

 

[richardbrennan]

Thank you all for the information and suggestions.

I am a member of the WOA and I am making inquiries through the forum and email group. I shall also contact Solent Welding to see if they can help; Trafalgar Yacht services are on their annual holiday at present and not back until the 27th.

I think the next step is getting the mast down and dismantling the saloon table as the support goes through it. The table does not look like an easy job as I don't think it was ever designed to come out once the boat was built.

 

[Chris_Robb]

Thank you all for the information and suggestions.

I am a member of the WOA and I am making inquiries through the forum and email group. I shall also contact Solent Welding to see if they can help; Trafalgar Yacht services are on their annual holiday at present and not back until the 27th.

I think the next step is getting the mast down and dismantling the saloon table as the support goes through it. The table does not look like an easy job as I don't think it was ever designed to come out once the boat was built.

Another problem common with mast supports is where they mount. My Westerly Oceanlord mast support was crushing the base, and this needed to be reinforced by a SS channel over the top to spread the load better. Worth having a look at whilst doing the work.

 

[richardbrennan]

Many thanks for that, I'll check it all out once I get the table and original support out.