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To all,

I wanted to take my time to talk about the dramatic failure of the foremast case on my Tiki38 Pilgrim last saturday.

here is what happened: Going upwind in a 25/30 knots of wind, one reef in each sail, speed 7/8 knots, choppy water. Fast and tight.

As soon I noticed slack in the leeward shrouds and the mast case movin laterally, the case boke in 4 different places and the mast went down between the hulls. We managed to get everything back on the boat and lost nothing. Foredeck + mast case have to be rebuilt. Pilgrim will be hauled out tomorrow.

I called James Wharram the next day and got Hanekke on the phone. She knows me, and actually was waiting for my call as news go fast with the Internet. I emailed her pictures, and we rediscussed later.

We agreed on these points (from her email), and I appreciate very much her attention and openness about the problem:

"Thanks for keeping me informed. The photos are very clear. I think the breakage is a combination of

1) structure not enough safety factor

2) fatigue in the plywood after many cycles of pumping action in chop and waves

3) boat being sailed hard regularly

The structure has stood up for many years, but has eventually failed. We need to get a structure with high enough safety factor. I think the beefing up of the step with the extra pieces of hardwood will have done enough to strengthen it, but maybe a different design would be better still."

I want to add this: Aluminium masts are fine but have a tendancy to "pump" in heavy winds. So, I think there was also a resonance factor with chop, tight sheets and mast "pumping" which completely destroyed the box.

I will clean and rebuild, certainly with an improved design for the box, including materials like carbon and may be a dolphin striker.

To all T38 sailors: When going upwind, don't push too hard and keep an eye on your foremast.

To all T38 builders: you can already think about add strength to your box. It is not that difficult to do at this stage. I will keep you informed how the fix will go.

Cheers.

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Jacques,

Thanks for the information and updates. This specific issue was addressed a little over a year ago in this forum.

http://wharrambuilders.ning.com/forum/topics/tiki-38-owners-reinfor...

Wharram sent out an update to the plans for reinforcement of the mast case.

However, I must disagree with the assertion that an aluminum mast's pumping action will have any more cause in this issue than a wooden mast. I have had both wooden and aluminum masted Wharrams, and I can say with certainty that the wood masts would pump far harder and with significantly more energy than the aluminum masts ever did.

The mast case on the original plans is simply under engineered. The remedy is easy and the remainder of the Tiki 38 design appears to be well engineered.

Here they are

Attachments:

Jacques,

    Please take many pics of your repair and offer suggestions for preventing this problem for others to learn from.  As you know, we modified our forward mast case and Wharrams have modified the plans for the Tiki 46 based on our findings.  They saw our modifications and approved them and, more importantly, the ocean sailing we have done since then has tested our modifications and found no further weakness. 

    Any structure on the water or also on the land requires close and regular inspection to locate and then repair areas of wear and to make improvements to the basic structure if needed.  I have never lived in a house that did not need structural repair and the same with all the boats I ever owned as well.  It is most helpful to know where to look.  On our boat almost all the structural areas of concern were in the foremast case area and we doubled some of the structure there and increased the fillets underneath the mast (from the dinghy) and Nev and Wharrams discussed this area in detail.  I am sure these changes can be obtained from the design office.

    Once you have built a Wharram, you know how to inspect and how to fix and you just keep some epoxy and fiberglass and a bit of spare ply and hardwood available.  We have even used these materials to repair houses and Jacques used these materials to repair his now famous Jeep.  Structures "work" and need to be repaired.  It is great when you can make these repairs yourself where ever you go with just simple things and a bit of skill and epoxy/fiberglass construction.

     Ann and Nev

Lucky thing you were not mid-Atlantic at the time. Of course this is a good time to have two masts instead of one . Your options are so much expanded if you got something aloft to work with. Does the same problem apply to the mizzenmast case?

One thing to be warry of is the throw carbon at it instinct.  Great materials, works well with wood, etc....  But...   You have have to know what you are doing and have an engineered solution to it.  Carbon it tremendously stiff, and if it is added haphazardly to a wooden structure, can end up picking up all the loads, but not being structured strongly enough to actually carry these loads long term.  You get a big unexpected bang.  This kind of failure happens to weekend warriors, and happens on cup boats that loose a nose.

If you are using enough carbon to carry all the loads, wonderful, but short of that you have to have a very food handle on how the loads will be shared, and intuitive solutions are often wrong.

On the other hand, you can radically strengthen the wooden parts, or toughen them up, with judicious thickening of existing parts, and armouring with appropriate glass.  Decisions on quality of materials; grain orientation (substituting strip planking in glass);  Using different ply arrangements (often the 1088 stuff is not as good for elements as it is for panels;  Assessing which material are stronger on what orientation; considering species; lam thicknesses.  These are pretty easy decisions to make on the fly and can have major effects.

Hi Jacques

Thanks for your posting. I am sorry for the damage Pilgrim has sustained. As a matter of interest if the mast was 'pumping', was it hitting the back brace of the mast case? I am very interested in this problem. Dragon is 10 years old and has done a fair amount of sailing, including days of ocean sailing to windward. I have not pushed her hard. I have (touch wood) not had issues with the mast case. I do keep a close eye on it as I have lengthened both my masts by a metre each and increased the sail area accordingly.

Dave

Hi Dave,

The mast was properly blocked sideways and on the rear by a system of pads made of rubber and plywood. Actually it was more a sideway problem, as you know, it is difficult to maintain a good tension on the shrouds on these boats, so, inevitably, on each tack, ther is sideway movements.
Another point, last year, i noticed a tiny crack under the case and put two strengteners under, they worked fine as it broke around, but they were too short. They should have been all over the length of the box.

For the new design, i think there are good gains to be made just playing with the underneath shape, which, if it was not straight, would be a lot stronger.
I have a friend who is a naval architect and will come with such a design.
Hello John,

The rear mast is another issue as it is on the mid beam. This beam does not cross the hulls like the others, so there are importants efforts on the rear one as the inside of the hulls tend to get pressed under the compression loads. This has been already discussed here and is a matter too.

Well, knowing where the weakness are will help everybody to deal with them.

Hi Jacques

On Dragon I put an aluminium tube with seagull striker across the bows to take the forestay. I didnt like the bridle design as drawn in the plans as it could pull the hulls inward and be difficult to maintain rig tension.

On a day sail I noticed that the rig was slack and when I checked I found the seagull striker cable was slack and the tube was flexing  leading to the mast leaning against the sides and rear of the mast case. I was really worried about these loads and sailed very carefully back to moorings to retension the cable and add locking nuts. I havent had the problem since. What I fear is when the mast leans backward and touches the back plate it puts force on the back of the mast case, this is a massive lever imposing loads on the back of the mast case which could lead it to fail. Particularly as this is a dynamic force if the mast is 'pumping' in a seaway.

From Brazil to Grenada we had many days hard on the wind bashing into the seas, and there was no sign of trouble (where were the trade winds?!!. )On my leg from Fiji to NZ we had 5 days of beating into nasty seas, triple reefed most of the time. There was no sign of untoward stress. If the mast case had gone, it would have been a long, slow trip home!!

However altho we havent picked up trouble yet, the mast case is lightly designed and should be beefed up from the outset.

I hope your repairs go well and your back sailing soon!

Dave

Jacques said:

Hi Dave,

The mast was properly blocked sideways and on the rear by a system of pads made of rubber and plywood. Actually it was more a sideway problem, as you know, it is difficult to maintain a good tension on the shrouds on these boats, so, inevitably, on each tack, ther is sideway movements.
Another point, last year, i noticed a tiny crack under the case and put two strengteners under, they worked fine as it broke around, but they were too short. They should have been all over the length of the box.

For the new design, i think there are good gains to be made just playing with the underneath shape, which, if it was not straight, would be a lot stronger.
I have a friend who is a naval architect and will come with such a design.
To me, rig tension is difficult because mast is basically lying on the beams, but shrouds are attached to the hulls. As there is flexibility between the two, there cannot be stable tension.
No?

Hi Jacques

You are right, you cant get a tight rig as on a monohull. It is a bit pointless trying as the boat does not need a tight rig.

This is just my preference on my boat and that is to keep the forestay tight enough so that the mast does not ever touch the back plate. There is enough of a gap in the mast case either side of the mast so that when it does lean over a bit side ways, it doesnt touch the top of the mast case, or if it does there is not much load.

My current cruising area is really protected and until the postings of the various mast case failures, I had not given it much thought. If I ever do any more offshore passaging, I will beef up the mast case!!

All the best.

Dave

Dave,

I totally agree with not using shims between the mast and the top of the case;  there is no way even a very strongly built case could restrain the sideways loads of the foremast under sail.  In fact,  those forces may have been instrumental in several failures.  I keep the rigging on Kattu tuned so there is an equal gap behind the mast as at the sides,  and the mast never touches the case even in heavy weather.   I also agree that the rigging should not be overly tight;  there is no advantage to that on the wingsail rig and tight rigging adds to the compression load at the mast step. 

I checked out Wharram's improvements to the mast case,  and perhaps they do not go far enough.  When building Kattu's mast case,  I increased the sides thickness to 18 mm,  and increased the overall depth of the sides from 280 mm to 406 mm,  so that the bottom of the case is flush with the bottom of the beams.  This makes for a vastly stronger truss,  which in effect the case is.  It also provided nice chain fall from the windlass,  with the chain storage imediately below and forward of the windlass instead of in front of the mast....automatic chain feed in or out and the weight is further from the bows.  Mostly I stuck to the plans,  but when I saw the foremast case drawings my intuition kicked in and said "make that much stronger"....I'm so glad I listened!

-Alf

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