Small Power Trimarans

I can easily understand the use if training wheels (amas) on a sail boat , that the wind is trying to tip over.

But with a proper placement of mass a slender monohull of even 12-1 LB ratio should be steady enough not to need stabilizing help.

So why a Power Tri??
What is gained from the configuration that a similar monohull is lacking? Is the size so small that extra deck space is the bonus?

FAST FRED

 

Deck space.... well, for adding a sunpad, I guess. Could reduce the rolling inherent to long slim monos. Also the coolness factor.

 

on heavy bigger boats yes, but in a very slender full load small boat with OB CG wont stay down i figger

 

Small Power Tri

Here's one I remember seeing an ad for in Power Multihulls. The reason I remember it in particular is I know the fellow who owns it. I thought he was trying to sell these units as a dealer, but I just talked with him today, and he indicated there was only one built by some guy down in Miami. He will try to send me more info before he leaves for vacation. He lives in OC Md

Appears to be a nice looking design

 

The Landau Launch Company designed their twin tunnel technology some years ago http://www.selectyachts.co.uk/landauhome.asp?ArtID=261 and now market the Landau 29 as a Category B offshore cruiser. http://www.selectyachts.co.uk/landauhome.asp?ArtID=16

It's an interesting craft in that the bow wave is swallowed by the two sponsons, which results in almost no wake when traveling at displacement speeds. Being certified for use in winds up to force 8, the crew in the 29 is likely to want to give up before the boat does.

Pericles

 

"Could reduce the rolling inherent to long slim monos."

But that would give the boat a "multihull ride,

rapid vertical accelerations, rather than the far more sea kindly and easier on the folks skinney hull rolling ride.

Some of the power round the world boats were tri configuration. Thousands of pounds of low machinery , so why the training wheels?

FF

 

Fred,

The rationale for the Landau 20 was to produce a very low disturbance hull form for cruising at displacement speeds and it is extremely good at that. The bow wave is swallowed by the twin tunnels and leaves very little wake. Better than displacement hulls at the same speeds.

"The Landau concept is based on a unique hull form designed by top yacht designer David Thomas. The revolutionary ‘twin tunnel’ shape offers uncompromised stability along with the benefit of producing minimal wash at all speeds.

The conventional bow profile opens out to present wake eating tunnels. The wash created by the bow section is swallowed into the tunnels and released at the transom with virtually no wash at speeds of up to 8 knots."

However, just like Topsy "who growed & growed", the hull form was also able to plane quickly and easily, so eventually along came the Landau 29, a Category B RCD certified offshore craft capable of handling waves up to 4 metres (13 feet) in height. Whether driving on the road or at sea, sensible people drive according to the road conditions or sea state. What I would say is that a car capable of more than 180 mph will have safer tyres, suspension and brakes and better able to stop the vehicle at 30 mph than a more mundane car. And so it is with boats. Anything more than a flat calm`most boats stay in the marina, but those owners who do venture out, appreciate the safety engineered into their craft.

Rapid vertical acceleration is a result of what? The height of the waves or the speed of the boat. If stabilisers are necessary to control the rolling of skinny boats, maybe skinny boats should be beamier? Everything in life is a compromise. Fate is the hand of cards you are dealt. Destiny is the way you play them. I would just like to go to sea with a full deck and a winning hand.

Regards,

Pericles

 

In the bigger boats, maybe. But try building a 60' mono with a 20:1 length/beam ratio, see what its motion looks like. The point of a power tri is to have much slimmer hulls than is possible with a mono, thus reducing wave drag and reducing fuel consumption while increasing cruise speed.
In the little boats, though, like the one by Chris we've been discussing... people are heavy and like to sit high, and an outboard isn't exactly heavy and low. A mono of the proportions of the main hull of Chris Ostlind's drawings would roll so much as to be downright scary for the passengers.

 

Pragmatic purpose

For a reality check and as a starting point for a boat of this type, I took some serious cues from Jim Antrim's 62' Duffy Voyager design. http://www.antrimdesign.com/electricboats/

This boat is a speed machine for a solo occupant with a hi-tech electric drive system. It carries a sizeable, heavy battery bank, nicely centered as low as possible in the hull for the issues you mentioned and still, it uses a fairly wide set amas for ultimate stability in a seaway. Admittedly, it's just about 30" wide and 62' in length. It also has only one guy onboard and he gets to sit well down in the hull in an enlosed cockpit. I just had to recognize some basic issues when I started and this boat became a good example of design thinking.

In attempting to design a boat such as the SurfBus that would be relatively easy to get on the water, operate by less than techy owners and drivers and have straight-forward, outboard motor serviceability, I soon discovered that there would be a price to pay for having such a narrow and efficient hull that could carry four people. That price came in the form of the stabilization needs and the ama setup was the simplest, most direct solution available to me if I wanted to maintain the design brief positon of an easily driven hull with exceptional fuel economy.

The boat could be constructed with an inboard engine set well down in the hull along with fuel tankage and other considerations for inherent ballasting. It would still be squirelly to some degree and require a good deal of care when turning in anything other than a calm sea. A totally calm sea state does not, typically, go together with good surf conditions; The principal reason for the design.

I would give away the ability to rotate the prop up and out of the water, thus taking away some of the beachability along with the easy familiarity of outboards in general compared to less common inboards. Parts for inevitable service would become an issue in remote surf villages, as well, compared to the ever-present outboards.

The SurfBus is only 53" BOA with a 40" BWL riding on a 28' LOA yielding an 8.4:1 hull. As an example of a high performance, non-outriggered, Very Slender Vessel (VSV) designed power boat, take a look at the 16m LOA Vosper Thornycroft built design that sports a B/L ratio of 5.7:1 These guys spent a lot of time defining just how slender they could go and retain stability in a wide variety of sea states and they settled in at the above figure. Why would I try to get a much more slender design to do similar things without the inclusion of amas for stability?

Agreed, the VT design has less in the water than the stated BOA figure, but it also has included sponsons in hull structure well aft in lieu of amas. It is propelled by a very serious pair of 700+ hp engines and surface drives, all out of the question for a boat such as I have designed for surfing adventures. I would like to get a ride on one of them, though. That would have to be one of the real E-ticket excursions on the water.

Perhaps the real issue here is in the reference to the trimaran configuration as having "training wheels" and not the choices that have been made for pragmatic usefulness?

I admit that some of the design solutions were derived for purposes of the aesthetic factors as I see them... but what boat is not subject to that requirement? I kinda like this boat. It has a certain dock appeal, if you will, for other uses beyond its original design application and it could be used, comfortably, in the manner I indicated in an earlier posting when I first showed it.

 

The Tampa Tribune just did an article about a power tri. It seems that an adventurous fellow from Auckland NZ is planning to go round the world in 65 days more or less. The boat must be for real because he has driven it from NZ to Florida. Might find some more info at the Tribune web site.

 

Chris, I think as long as your designs stray from simple, conventional monohulls, you will always have detractors. Some people just don't like multis, others are convinced there's no point to them. In the case of your "SurfBus", I think the tri hullform is a good one and would suit your design brief well. As well as being way cool. Whatever. My point is, keep thinking like you are, don't let tradition get in the way of new ideas that just might prove really interesting.

Fred, I'll fire back at you: What does a mono along similar lines to the SurfBus offer, that the tri does not?

 

The Vosper VSV concept is similar to that which I proposed for my Slender RIB - and whilst w'ere trotting out catchy names, I called it the Monomaran.... a slender displaning catamaran hullform, but only one of them.
Where the VSV differs from my project - just as it does with Chris's - is that the VSV is way more extreme (and let's face it way cooler too!)
Where the VSV incorporates sponsons built in as part of the hull structure, I have chosen to use inflatable tubes. These will provide enormous stability and buoyancy when required, but will allow the craft to be a practical tender.
It's definitely in the development stages thus far - I've done nothing beyond the initial model to give picture to my ideas at this stage....
I got a little carried away with the idea and added outriggers for rowing, and oars that would double as handles, which when combined with drop-down wheels on the transom will make for easy beaching or short portages ashore...

 

In the bigger boats, maybe. But try building a 60' mono with a 20:1 length/beam ratio, see what its motion looks like.
The point of a power tri is to have much slimmer hulls than is possible with a mono, thus reducing wave drag and reducing fuel consumption while increasing cruise speed.

The point is that few would ever build a 20-1 LB boat as the wetted surface would be really a detriment to fast travel., with low power.
The resistance to foward motion is Both wave making AND skin friction.

There is a point where getting slimmer costs speed , even though the waves are smaller.


Fred, I'll fire back at you: What does a mono along similar lines to the SurfBus offer, that the tri does not?

Less hull resistance 1 hull instead of 3 . Better motion as the craft is not jerked level with the unlevel water surface , in offshore waves.

I had built a Hedly Nichol 45ft "Voyager" in the '60's and sailed it for years thru the Carib, and am a multihull supporter.

However the multi hull operating characteristics are real , the motion is VASTLY different (QUICKER) from a monohull.

Smooth ride in big waves is not a multihull virtue , although the lack of heel is nice .

With a skinny power boat that is big enough to have good stability from weight placement (can survive a knockdown) , why slow it down with training wheels? And accept the Miserable top of every big wave motion?

If stabilisers are necessary to control the rolling of skinny boats, maybe skinny boats should be beamier?

Added stabisers is more use full for fat box boats , where the hull lifts to severe angles as the wave hits the beam , as the leverage of wide beam adds to the rolling forces. Box boats are great kept in port ,but extra lively in any sort of a seaway.

Just watch a log and a box in a seaway , which would be better at keeping lunch down if enlarged to 50 ft and you were on board?

FF

 

Wave Piercing Trimarans

John Holtrop has plans for his 15' and 18' wave piercing Trident trimarans.
The 15 ft. version will plane with an 25 Hp outboard.

http://www.johnsboatstuff.com/Boat Designs/TRIdent 12/wp-10.htm

http://www.johnsboatstuff.com/Boat Designs/TRIdent 18/wp-18.htm

http://www.johnsboatstuff.com/Boat Designs/TRIdent 12/renderin.htm

Some photos of this design can be found in this forum at

http://boatdesign.net/forums/showthread.php?t=11091&highlight=stitch trimaran