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Two months ago while soloing a different H17 on a 20 to 25+ knot day, I pitch-poled, the mast flooded and went turtle. Even with a helping powerboat, under the conditions we couldn’t get the boat up until we were blown to the far shore. It got dark, no lights, tide going out, bare feet cut in coral, damage to a wing, wife was worried and mad as hell, etc.
The curve in the chart for “with TORUS™” shows that beginning at a Heel Angle of about 30 degrees when the pontoon hits the water, the Righting Moment increases dramatically and maximizes at 45 degrees (with the flying hull about 4-1/2 feet above the water). Thus significantly increased stability is provided just when you might be in deep kimchee (between Heel Angles 30 to 60 degrees) giving you time to de-power sails or get crew windward.
Do-It-Yourself: Capsize prevention system (TORUS) for the Hobie 17 Catamaran
Introducing TORUS™ (Tip Over Resisting and Uprighting System) for the Hobie 17. Here's a system that promises to make catamaran sailing more accessable for those that feel capsizing is not an option. Read how inventor Ron Darby has solved his capsize problems on the Hobie 17...
For 33 years I have lived on year-around warm, windy and relatively flat Kaneohe Bay on Oahu, Hawaii. I have enjoyed all kinds of sail boating on the Bay including sailboards and full keel monohulls. However, since my son-in-law started bringing Hobies here about 16 years ago, I spend most of the time fooling with them.
I started soloing his Hobie 17 and a few years ago I was humbled with capsizing, and though the buoyant mast stopped the turtling, I could not get it up without the help of a passing boat. I’m 158 lbs. & 71 yrs. and just couldn’t overcome the windage from the tramps and upper hull.
Two months ago while soloing a different H17 on a 20 to 25+ knot day, I pitch-poled, the mast flooded and went turtle. Even with a helping powerboat, under the conditions we couldn’t get the boat up until we were blown to the far shore. It got dark, no lights, tide going out, bare feet cut in coral, damage to a wing, wife was worried and mad as hell, etc.
I want to sail in our windier weather and enjoy the high speeds as well as practice hull flying, but lessen the probability of capsizing and easier righting if I capsize. So I’ve began experimenting with the idea of placing pontoons so that they do not touch water until the heel angle is about 30 degrees when the Hobie wing starts to drag in the water and only then provide reserve stability. The pontoons are also located so that if you did capsize (not turtle), the submerged pontoon will provide significant righting moments. The pontoons are also to serve as seat backs to the wing seats to lessen fatigue on your lower back.
My first pontoon prototype used Styrofoam (Figure 1) and was tested on a squally day by two younger guys and me. Though these tests were very satisfying, I want pontoons that are lighter, more rugged, more user friendly, sexier looking, easier to mount and dismount, etc.
The second prototype, Mod 2, had an eight-foot long inflatable PVC pontoon (Figure 2) with 300 lbs. buoyancy (made for personal fly-fishing rafts). It was in this test I pitch-poled while I was checking the temporary tie-downs to the Hobie wings and suddenly was thrown into the sail. I heard cracking sounds – my ribs or battens? (fortunately both were OK; the cracking sounds I guess were from the battens moving in the batten tips).
Time to re-group – Mod 3 (Figures 3 and 4) has a large mast float (made from a 15-1/2 inch mooring buoy) and two new pontoons (not yet permanently mounted). A new pontoon support system will be used because I suspect that the supports on Mod 2 overly disrupted the water flow as they entered the waves and may have contributed to pitch poling under the high wind.
Because there are a lot of options and decisions concerning pontoon size, shape, support and location, I made calculations to guide me. The chart (Figure 5) is a plot of Righting Moment vs. Heel Angle for the Hobie 17 (if anyone knows me of similar charts using probably better formulas, please let me know). TORUS™ (Tip Over Resisting and Uprighting System) is the name for the high mounted pontoon idea. Positive Righting Moment is the effect of various weights of different items on the boat at different distances from the pivot point at the center of buoyancy tending to keep the boat upright.
From the chart it can be shown that when the cat is sitting flat (Heel Angle = 0) the boat is stable and the Righting Moment is zero. As the wind moves the boat, both hulls stay in the water until about 10 to 12 degrees of Heel Angle. During this period the boat is a true catamaran with the leeward hull providing the needed buoyancy as the windward hull rises higher in the water. After about 10 to 12 degrees of Heel Angle the windward hull leaves the water.
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In this region with TORUS™ you are sailing a good old cat again - you have a new downwind ‘hull’ (the pontoon). My calcs show that the righting moments in the chart “with TORUS™” are greater than those from hiking out on the trapeze from the wings while soloing. Of course you wouldn’t be going as fast because of the additional drag caused by the pontoon.
In the worst-case scenario the boat does capsize. The chart shows that the math model assumes that the crew is off the boat at Heel Angles greater than 60 degrees. The masthead float doesn’t get into the water until about 100 degrees of Heel Angle. The chart shows the positive effect of the masthead float if it is only half way submerged at 100 degrees, while at 110 degrees it shows the potential effect if the float is completely submerged.
The submerged TORUS™ pontoon provides approximately the same Righting Moment as a 2nd crewmember weighing 160 lbs. using a typical righting line system. In the chart it can be sensed that the H17 with TORUS™ is floating much higher and has a much greater probability of getting wind under the sail to right the boat. Note that this math model assumes that the mast neither floods nor provides positive buoyancy.
The H17 with TORUS™ should be trailerable by reversing the wings with the pontoons in place. However, the inflatable pontoons can be removed in seconds by unsnapping the clasps on the straps. It is a goal to have the pontoon supports also readily removable with wing nuts. The inflatable PVC pontoons so far are proving to be rugged. Other goals are to be able to sit on the pontoons and to hike-out on the pontoons using a trapeze. Also the pontoons may work as rollers for launching and beaching cats with symmetrical hulls.
TORUS™ should provide a stimulus so more people will become involved in beachcats when there is concern or fear of capsizing and entering “unfriendly” water (real or perceived) and uprighting the boat. Examples of such people and concerns are:
- wary would-be sailors venturing into purchasing a beach catamaran (or taking sailing lessons).
- experienced sailors desiring to feel more comfortable in inviting basically non-sailors to crew, e.g. the wife, children, grandchildren and the family dog as well as when carrying an outboard motor and extra gear, e.g. ice chests, lawn chairs, hibachis, etc.
- sailors who are considering moving up into more exciting boats or adding ‘go-fasts’ to their existing boat (e.g. jibs, spinnakers, spinnaker poles, wings, trapezes, etc.) can ‘calibrate’ themselves by sensing the angles-of-heel for different wind and wave conditions where capsizing normally occurs by installing TORUS™ on only one side and hiking-out in a typical manner on the other side and watching for the leeward TORUS™ pontoon just ‘kissing’ the water surface.
- experienced sailors hesitating to go sailing in marginal weather when there may be insufficient crew on board to keep the boat upright should the wind and sea increase.
- experienced sailors and crew who want to encounter a new dimension in sailing ‘social’ beach catamarans (without kids, pets, coolers, etc. on board) where they may trapeze from the TORUS™ pontoons gaining significantly more righting moment.
My immediate concern is in modifying my H17 for my use. I will keep the group informed about tests of Mod 3. Does anyone know if this idea has been tried before? If there is enough demand, conceivably a company may be found to provide TORUS™ type things for other beachcats with wings. I would appreciate any interest, questions and comments from anybody in the group.
Aloha & thanks, Ron Darby
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Comments
Add a new commentWishing there was a way to access the pictures, graphs and figures?
Alan