Thoughts on a self-righting multihull

As seen in the GREAT photos posted by Clipper (below), one of the downsides of rc multihulls is the chance of capsize & subsequent rescue. I have experienced this myself with my early attempt at a 1m trimaran
( ) and it’s NO FUN.

I’ve had a number of ideas for the use of movable balast, etc as a means of provide righting moment, but they all seemed too cumbersome & likely to fail.

So , imagine a “Team Phillips” concept catamaran with twin wingmast rigs
stepped over each hull. If the wingmasts were built out of a foam cored composite, adequate flotation could be inherently provided in the design. Thus, the boat would come to rest on it’s side & not turtle. Hopefully the upper rig would receive a puff of wind that would cause the craft to get upright again. If this did not occur, it would be possible to have the sidestays on a motorized 3rd channel “loop” that would cant the masts in a manner to force the lower mast down & cause the boat to get on its feet.

Any thoughts as to whether or not this would work?


It seems reasonably self-evident that it would, provided the ‘flipped’ CG does not get on the wrong side of the ‘flipped’ stability curve.


Do the mast need to be upright: canting them outwards would move the CG toward the ‘recovery’ side.

You should be able to use the unimmersed side of the rig to generate lift, which should help the righting process, if the sheeting arrangements were right.

Just maundering


Bill -

part of the problem when a multihull has been tipped on it’s side resides in it’s total width. Often, in an effort to reduce tipping tendency (not pitchpole), beams become exagerated, and the mast base is usually much higher off the wateer than the mast tip - thus the boat has taken on a very stable “tripod” effect. Simply lay your landyacht on it’s side and you will see what I mean. The two wheels (rear and front) are one part of triangle and tip of mast on ground is the other - a very stable base.

Likewise on a multi (cat or tri) - is the distance from the water to the mast base and also to the tip of mast. If (?) you could position a mast only on the hull laying on the water, the mast would float and support the platform (it being vertical), and the wind would take the platform, if it had any kind of mesh fabric resistance and rotate it around so the mast tip was pointing toward the wind. Hopefully a bit of wind under the sail lying on the water, and a bit of a wind gust against the trampoline in the air would product a self-rescue effort (or a partial effort). Unfortunately, the mast/sail on the top hull still vertical in the air would cause an opposite rotation with the top hull and mast trying to drop down to water level and the entire platform becoming inverted. The water level mast would be trying to resist this rotation. Not sure which would win, although I suspect the mast/sail on the water would have sufficient surface area to resist the weight aloft.

Two possibilities - both requiring easy engineering, but a third servo function - would be to allow the cross beams to be hinged, to allow the hull in the air to fall off and be lowered toward the water, thus increasing righting moment and self rescue. The other would be to have the ability to tip the mast(s) by lengthening the the water-side shrouds which would also allow the aiirborne hull to tip back towards the water - in eitehr case allowing the airborne hull to act as a longer lever to hopefully right the boat. Then retrim the masts to vertical.

I have considered both methods, and lean toward the “water” hull to be canted and then repositioned after righting, instead of fooling with masts and if they really are vertical after recovery - or are they off a bit. Being able to fold the bottom of the water hull toward the beam (eiter cat or tri) might be able to transfer enough weight to the top hull and lever it back down. Then a release/reverse of the folding to bring the hull back perpendicular to the beams. I think one would still require some type of masthead float to preven a “turtle” - but foam masts might eliminate that. The biggest effect is to make stuff relocate to get the upper float/hull to act as a lever. If one didn’t fold the beams at the floats, perhaps a beam hinge close to center of the beam would be workable too. Unfortunately, some system must also extend the windward shroud to allow the hull/float to drop towards the water.

On the big (full-size) “Supercat” catamarans (12 foot beam x 20 feet long), the mast base was pinned to the mast step ball, and shroud extenders on the windward hull (in the air) lengthened the shourd about 14 inches, and once righted, there was a lever which re-tightened the shroud and the shroud pin could be then be replaced bringing mast back to vertical. Being able to do this on the water would be the required engineering part of the process.

If the first part isn’t undertood - let me know and I’ll post a sketch of my thoughts/view.

Angus & Dick,
Thanks for the very useful comments. So the key issues are keeping the CG on the “right” side & using the upper rig as a way to generate lift.

Keeping the CG low presents a problem in that the “control pod” will possibly be hitting water at times. Dick’s hinged platform idea solves this problem rather nicely, but could be complicated. However if the masts are canted (with adequate buoyancy), the dunking of the lower hull will also cause the Cg to shift over to the other side & the boat will “flop” upright.BTW, Dick, I think the “waterside shrouds” need to be tightened, not loosened. Also, the shrouds will be between the 2 rigs in a big “X” with a compression post at the hound. Similar to Greg Kesterman’s Hobie Trifoiler. see below

Causing the upper “dry” rig to create lift presents other problems. Assume that the boat will “weathervane” with the hulls are downwind & the rig upwind. Gravity will initially cause it to rotate into a camber that will create negative lift. Upward lift will not occur until it’s tilted high enough for wind to get underneath. Canting the masts will make this even harder to overcome initially, but at some point it will be able to reach a tipping point if the design is balanced.
Angus, your thought about the rigs canting out is well taken. They couldn’t be significantlly tipped however at the risk of creating a vertical lift component. But it might not take much (say 2") to make enough difference & the upper rig would be helped as well.

Another potential problem would be if the lower sail gets loaded up with water, but it should be able to shed it if sheeted out.

Hmmm, maybe it’s time to clear off a workbench & get ready for a winter project…

Bill - here’s a thought to further confuse you… :smiley:

1999 - WRC2 was a catamaran, with two airfoils one on each hull and with a profiled joining. When sailing, the airfoil on the weather side reach 30° inside gradient versus a vertical axis and at the same time the other airfoil on the lee side has 30° outside gradient versus a horizontal axis. The lee side airfoil and the profile joining generate a lift. The in flight stability was controlled by a horizontal stabilizer in order to keep the rudders in the water.

This model was made at 2 Meter size.

Was this thing actually ever built? IMHO, it would be really difficult to control the horizontal wing well enough to be of much benefit. Plus, you’re creating alot more drag for questionable benefit. The same structure could instead be put towards forward movement, which brings us back to the Team Phillips/Trifoiler concept. Also, these types of things are usually being optimized for one-way speed runs, not any sort of around-the-buoys racing or general sailing.

It is my understanding it was built and tested. There were three guys experimenting with concepts of getting sailing craft up and out of the water, without drag and limited top speed calculated for hydrofoil equipped craft. These guys are (or were) deep into WIG theory (WIG = Wing In GroundEffect) or a cross between hovercraft and an aircraft. A WIG craft sits on a cushion of air, but this cushion is created by aerodynamics rather than by an engine. This means that it only exists when the WIG craft has sufficient forward speed. This is called a dynamic air cushion as opposed to the hovercrafts static air cushion. Here are a couple of their experimental craft…

The original idea

failed for two stated reasons … 1) the wing, when it touched the water created too much drag, and …2) the model was built too light.

They were working toward getting something to move across the water fast enough for aerodynamiccs to replace the ground effects of normal WIG conceptual craft.

Interesting stuff - do a Google search.

ummmm - all three work for Airbus … engineers !

So, Dick, getting back to the topic, what ideas have you had or heard about regarding self righting multis?

I seem to recall that the old Pop Up cat claimed such an ability.

Dang - knew you would eventually ask!

I’ve searched everywhere and am unable to find any photos of the cat and specifically it’s method of self-righting. I recall it was done via folding/hinged cross beams, and there is where my knowledge ends. Part of the problem was old Herb wasn’t really the friendliest guy about sharing info, and $3.00 sent in for plans got you some sketches and a 4x6 inch colored photo of all his boats on land - his advertising photo. I was (at the time) specifically after the purchase of plans for the wingsail he had in photo, but he refused to sell me wing - or plans. Indicated my boat at 48 inches was too small (his were 50" as I recall :mad: ) so anyway, the correspondence died, he sold his business and I have yet to write to the supposed new owners.

Maybe I should start a few different forum posts to see if I can find anyone who ever may have purchased a cat from him?

Anyone know someone who knows someone that had one?

For (non-sail) ground effect craft, try googling for ‘caspian monsters’ ( or ‘ekranoplan’. Purely entertainment - but what beasts!


If the rig is light enough then it should only take a small amount of buoyancy at the tip to keep the boat on its side. Windage should take care of the rest as the hulls blow around to the downwind side and the boat flips up again…

In theory, havent tried it yet, maybe a ping pong ball?!