A Photo & Discussion Forum for Wharram Design Enthusiasts
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.
Sorry Alf, I just realize that there is a foto in the blog already. That answers my question.CCheersHelles
Alf Bangert said:
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!
Well done its a beautiful job!