Small Powerboat Seakeeping [Archive]

intrepid71

01-07-2005, 09:06 AM

From my own boating experience, I have found that passenger comfort aboard small powerboats traveling at speed through moderate to rough coastal sea conditions often leaves much to be desired. Small powerboats that fall in the 16 to 25 ft range are possibly the most popular of all recreational boat categories. Since many of these boats are operated on bodies of water large enough for a stiff afternoon breeze to kick up sea conditions that make traveling at cruising speed uncomfortable, it seems to me that this is an area in the field of boat design where significant improvement would be welcome.

The first place to start would be to explore the current state of the art. With that in mind I pose the following query: For a modest sized powerboat, say 22 ft., traveling at 30 knots in 4ft wind chop sea conditions, what boat type or hull configuration would offer the smoothest, most comfortable ride?

The second question is an extension of the first. Are there any boat designs or configurations that are not currently on the mass market that may offer significant improvement over currently available types? For example hydrofoils come to mind as a possible way to effectively "decouple" a boat hull from a rough water surface. Is this an area that is ripe for innovation? Do you think boat buyers, both recreational and govt./commercial, would be willing to pay for extra for a boat design that can offer significantly improved seakeeping at speed in many sea conditions?

tom28571

01-07-2005, 09:47 AM

The best boat to run 30kts into 4' wind chop?

To me, 4' ain't no stinkin chop. Too many overstate the height of sea states. Not saying that you are doing that but 4' is pretty big stuff unless on the open ocean with widely spaced waves. Also if average waves are 4', then some will be much bigger, like 6' or so and these are the ones that you need to be concerned about. In closely spaced waves like that on shallower inland waters, most sensible people are ashore or running at reduced speed if they have to be out.

It may not be too difficult to come up with a boat that will do what you ask but what about its atributes and behavior in other situations?

Multihull?
Swath?
Foils?
Ground effect?
Sea sled - IVB?
Wave piercer?

All of these will probably have trouble at the length you want.

intrepid71

01-07-2005, 10:47 AM

Well, for one thing when I am saying 4 ft chop I am talking about about a wave with 4 ft height from trough to crest, some may consider that to be a 2 ft wave height. A true 4 ft wave with a steep 8 ft face is too much for any 22' powerboat to take at speed IMO.

My point of reference is from boating on the South Shore of Long Island. On a typical summer day, a brisk southwest breeze often sets up and by late afternoon, the Great South Bay get rather snotty, especially when boat wakes coming from every direction get combined with the wind sea. My parents have 40' wooden Chris Craft which cruises along at about 16 to 18 knots. In those conditions they will take spray over the flybridge and have a few good thuds along the way. My boat is a 22' Mako Semi Vee, and running above 20 knots in those same conditions I will get pummeled and completely soaked in the course of a 30 minute ride across the bay. If a passenger is on board it is an uncivilized ride to say the least. Now granted, a deep vee or cat would offer some improvement, but my experience with the deep-vee at least indicates that this is a moderate improvement only and the ride would still be uncomfortable.

Starting with this common experience on the Great South Bay I can then extrapolate for people who operate on larger and deeper bodies of water and I see a need for better seakeeping in small powerboats. Of course, I haven't sampled every type of small powerboat out there, but that is why I sent the original question out to the forum.

randy kahn

01-07-2005, 11:59 AM

Intrepid71, My expreience has proved a power cat (of good design) to be the best all around water craft for passenger comfort in the size range (and larger) that you decribed. I believe a real open water comparison, cat & mono-hull on the same day will always provide that proof. Please try it and let me know your opinion. Also choose a sloppy day you would not normally take your mono-hull outside so there will be no doubt. Thanks, Randy

intrepid71

01-07-2005, 01:38 PM

Randy,

Thanks for the reply. I suspected that the powercat hullform probably represents the current "state of the art" for seakeeping in a small powerboat. I imagine a displacement type such as Glacier Bay would likely offer the best ride although it would be a bit slower than the planing cats due to higher wetted surface. I have never taken a ride on one of these boats, but one day I would like to try it. I have read that while the ride is superior to a deep-vee, the cat form is not a cure-all and you will still get bounced pretty hard if the conditions are right. Of course this is true for any vessel, but I guess my point is that I am not sure that the power cat form represents the best possible solution.

When it comes to a truly smooth ride it seems to me that a fully submerged hydrofoil would have the most potential. Of course a traditional hydrofoil design has some serious drawbacks such as deep draft which would make it unsuitable for a small boat. What I am envisioning is a small hydrofoil boat with foils that would retract into the bottom, eliminating the draft problem. Furthermore, the retraction mechanism would be designed such that foils could be deployed or retracted while the boat was at speed, giving the operator full control over when and where he wanted to be in hydrofoil mode. For stabilty and trim while on foils, perhaps some sort of wand-style feedback control system could be used, similar to the Rave sailing hydrofoils. Finally, there is the problem of keeping the prop in the water as the hull rises up, which might be solved by putting an outboard on a vertically swinging pantogram bracket and have this synchronized with the foils being retracted or deployed. Of course, putting all of this mechanism into a small, lightweight package that doesn't ruin the aesthetics of the boat and cost a fortune will be quite a trick. I have wrestled with the idea for a while and have decided that it is beyond my design ability. That doesn't mean there isn't someone out there who couldn't pull it off. When you think of all the complicated mechanisms they fit into a car, it really isn't asking all that much.

tom28571

01-07-2005, 08:03 PM

mattotoole

01-07-2005, 11:10 PM

woodboat

01-07-2005, 11:48 PM

From a ride perspective on a small boat the best I have ever been in was my friends old 17' AMF crestliner. Closed bow, very deep V, no lifting strakes that I remember so it was a very smooth bottom. It would slice through waves like the edge of your hand in the bathtub :) It was reasonably fast, about 42 MPH with an inline 165 HP 6 cylinder. I raced him in some rough stuff. I had a 15 ft Mckee craft, solid boat, hull shaped similar to a whaler. I was flying out of the water, catching air, heck shaking my teeth loose. I finally had to give up. He just pushed the throttle down and pulled away. Turns out he didn't know I was racing and he simply was driving slower and waiting for me. I remember watching it slice through with everyone sitting comfortably as I slowed to a crawl. I think current designs go for more lift and efficiency from there high speed runabouts. Of course a retractable hydrofoil sounds cool :)

gerard baladi

01-08-2005, 12:59 AM

I have been looking for that perfect hull as well for the past year, as I encounter the same kind of sea and wind conditions described.

I am now looking at a Tunnel hull option 32' beam 8'6"(trailerable/twin 225Hp) . I am told that tunnel hulls are the cross of the 2 both worlds of deep V and Cats. Any comments?

What about Stolkraft Hull, has anybody tried them? They are so rare that I wonder why?

intrepid71

01-08-2005, 10:57 AM

My take on tunnel hull is that it is basically a cat with assymetrical hulls. From head on it looks like a deep-vee with a tunnel down the center. I believe the idea is to get the seakeeping of a cat with handling characteristics of a deep-vee. Specifically, the tendancy to bank into turns rather than away from them. I have never ridden in such a boat, but it seems like good idea. The following link shows a boat that may not be a true tunnel hull, but it does have assymetrical hulls:

http://www.corsairmarine.com/0FoilerIndex.htm

The other very interesting feature it has is a hydrofoil situated between the hulls for additional lift.

intrepid71

01-08-2005, 11:12 AM

What about Stolkraft Hull, has anybody tried them? They are so rare that I wonder why?

The main advantage of the Stolkraft hull is increased efficiency, I believe. I think they claim it has good seakeeping as well, but from the pictures I have seen it seems there will be plenty of relatively flat bottom area exposed to the waves at speed and usually that means pounding. I haven't ridden one so I can't say for sure.

As far as why they are so rare? It appears to be a complex hull shape which might be somewhat expensive to build. It is also not the prettiest shape in the world, which might limit its mass market appeal. Also it is patented design, which may be limiting its use. Perhaps the inventor is asking too much money.

intrepid71

01-08-2005, 11:27 AM

Cats used to be very popular in Australia, and probably still are. I rarely see them in North America though.

Some boats in this size range are advertised as having "seakeeping" hulls. This probably just means more deadrise than a typical runabout, but not quite deep-V. Am I right?

The max deadrise that you typically seein a small powerboat is 24 degrees at the stern. Anything more and you get diminishing returns and a tippy boat at rest. The amount of deadrise that is needed to make it a "seakeeping" hull is really however much the marketing people decide.

intrepid71

01-08-2005, 11:32 AM

[QUOTE=woodboat]From a ride perspective on a small boat the best I have ever been in was my friends old 17' AMF crestliner. Closed bow, very deep V, no lifting strakes that I remember so it was a very smooth bottom. It would slice through waves like the edge of your hand in the bathtub :) It was reasonably fast, about 42 MPH with an inline 165 HP 6 cylinder.

Yeah, removing the lifting strakes might help soften the ride. A nice heavy inboard also helps in giving a solid feeling ride, by putting more weight lower and forward of where an outboard would be.

intrepid71

01-08-2005, 12:27 PM

I agree with Randy that a multihull of some sort is probably the best compromise available right now.

As far as I know wave height has always universally been the vertical distance from trough to peak.

My main point was that a 22' boat that could excel in the conditions you described will surely be way less than optimum most of the time and next to useless some of the time. Of course, nothing is certain until you try, so go to it.

A small cat is great in waves some of the time but when the water hits the underbelly at speed, you better be hanging on.

Regarding wave height, surfers consider it to be the height of the crest above the mean water level. So a four foot wave to them will have an 8 ft face. When talking boats, I will stick to the trough to peak definition.

Regarding your second point, I would have to disagree. It seems to me that any boat that can handle rough seas at high speed is not going to have trouble when the water is glass flat or any condition in between. Perhaps it would not be as effeicient as a boat optimized for flat water, but it would hardly be "useless". Of course the opposite is not true, a boat optimized for flat water may in fact be useless (and dangerous) in rough water.

tom28571

01-08-2005, 03:22 PM

Regarding wave height, surfers consider it to be the height of the crest above the mean water level. So a four foot wave to them will have an 8 ft face. When talking boats, I will stick to the trough to peak definition.

Regarding your second point, I would have to disagree. It seems to me that any boat that can handle rough seas at high speed is not going to have trouble when the water is glass flat or any condition in between. Perhaps it would not be as effeicient as a boat optimized for flat water, but it would hardly be "useless". Of course the opposite is not true, a boat optimized for flat water may in fact be useless (and dangerous) in rough water.

I'm not surprised that surfers would have different terminology, but should that change hundreds of years of nautical usage?.

On the second part. I stick by what I said, not your interpretation of what I said. By "excel" in rough water, I meant "optimized", just as you apparently meant by the "optimized" flat water boat.

Richard Petersen

01-08-2005, 04:03 PM

Is a 24 degree constant deep V for about 65 % of the WL, with a cleaver bow about as slippery as I can make a woody of 21' ? It is 4' 6" wide. I have 30 days before construction begins. Conventional inboard -shaft-prop-rudder. Thanks.I can scan and send plans.

intrepid71

01-08-2005, 04:29 PM

I'm not surprised that surfers would have different terminology, but should that change hundreds of years of nautical usage?.

No, it shouldn't. I think we are in agreement on this, trough to peak for nautical usage.

On the second part. I stick by what I said, not your interpretation of what I said. By "excel" in rough water, I meant "optimized", just as you apparently meant by the "optimized" flat water boat.

I'm still not following you. Your post said that a boat designed to excel in the rough water conditions I described would be less than optimum most of the time and next to useless some of the time. In what conditions do you envision it would be next to useless? My point is this: a boat designed to perform well in rough water will also perform well in calm water. The opposite is not true.

Richard Petersen

01-08-2005, 04:52 PM

Sounds right to me.

tom28571

01-08-2005, 07:51 PM

I'm still not following you. Your post said that a boat designed to excel in the rough water conditions I described would be less than optimum most of the time and next to useless some of the time. In what conditions do you envision it would be next to useless? My point is this: a boat designed to perform well in rough water will also perform well in calm water. The opposite is not true.

OK, I'll type slowly.

The discussion started about far out designs like foilers and such in the attempt to make for easy riding speed in high "chop". A boat designed to be optimum in these conditions is very likely to be way less suitable in other conditions and speeds.

For instance: A 22 foot boat of even normal deep V of, say 26 degrees or so deadrise, is going to be tippy at the dock and a pig between about 6 and 20 knots. By pig I mean big wake, nose up, gas guzzling, hard steering and no fun to drive.

A foiler is not going to be very good unless it is on foils at speed and a problem around docks to boot and very sensitive totrim and overloading.
A cat that is optmum on the waves is likely to not steer or maneuver really well at low speed and is sensitive to overloading. Some of these problems can be treated by sophisticated design and controls much like the computer "fly by wire" systems on modern aircraft that are inherently so unstable that a pilot cannot even fly them without the computer.

That is what I meant, no more, no less. If there were any such boat design that did everything in excellent fashion, it would have been found by now and then designers would be out of work and we would have nothing to talk about.

Peace, I'm going to watch a basketball game.

Richard Petersen

01-08-2005, 08:02 PM

Tom!!! I never gave you permission to take my 2002 Chaparral 186 SSI with a 5.0L 220 hp out, and pass such truthfull judgement on the way it handles. Outstanding bit of truth. You forgot the prop blows out in a high speed turn. Still-- Very accurate! Rich.

tom28571

01-09-2005, 11:05 AM

Rich,

Actually, since it was your boat and you didn't know I had it out, I was afraid to put it into a tight high speed turn. :D

Seriously though, I suspect that if more buyers had the oportunity to observe this kind of behavior first hand before they sign the check, there would be fewer such boats sold. My brother in law bought a deep V 18 with 100hp Evinrude V4 last year and got me to go out with him afterwards. It had this exact behavior only a bit worse. It did not get on a full plane and comfortable to handle until it got to 22mph and topped out at 28mph. That's a decent use range of 6mph. :( Some deep V's are a lot better than others in this respect but I don't think they are a good choice as an all round boat.

Richard Petersen

01-09-2005, 11:59 AM

I am serious about the boat description at the top of this page. Does a Cleaver on the bow of a 21' make a big ride comfort change? I ride in old Hackers, Garwoods etc. Is their comfort due to +25' to35' and weight, warped design bottoms are almost flat. Or is there a magic combination in small 21' boats in a 2' to 3' chop. I could even pay you money! :) For a sincere effort.

Richard Petersen

01-09-2005, 12:07 PM

Better yet. Take it out on a busy weekend choppy day. I can not safely run with yachts or big cruisers. Water over the bow. 6 to 9:30 and 6 to sundown, Period.

Sean Herron

01-09-2005, 12:24 PM

Hello...

...is on the money here - I am not even going to consider foils for a high speed civilian powerboat - the feds will start making us all wear helmets... :)

As for historical development of good solid performing rough water deep vee boats you should have a good look at the lines - particularily the run of the buttocks - the antihedral in the main lifting strakes (not spray rails) of some of the late Don Arranow (DONZI) hulls and those of 'Sonny Levi'...

As Tom has said the only trouble with these boats is that they are inherently not designed for displacement speeds - at speeds where the hull will not get onto its bow wave they are pushing same out in front of themselves - on the sport boats I built for a number of years we had some success dropping the bow using a two tank freshwater system - transfer weight forward when running slow - and aft again when planing with trim tabs down...

Hollow bow sections are not the way to go here either as they will not maintain a constant pressure against the bow wave - they push the water aside and the hull drops - this can get excessive and annoying - a sharp convex vee with strakes seemed to be the best solution through testing...

As for blowing the prop in high speed turns this should not be a problem if the lift strake is good and wide and has 3 to 4 degrees of antihedral and a bit of negative flip down at the transom - and so long as you have good tabs - just dont hook the hydros backwards to the dash switch... :) - that made for a fun test day once...

See http://www.monaromarine.com/monaro21.htm - they may not be to everyones tastes but they sure were a good ride in big short chop - Dan Parker - the owner - based the hull lines on Arranow's 'Cigarette One'...

You can see Parkers influence on the 19 footer that I designed years ago while I was working for him - for kicks - but his boats were rock solid and had a huge operational curve and were stable at rest too...

OK...

SH.

Richard Petersen

01-09-2005, 01:49 PM

Why is it the old woodies handle the chop better? Actually, they do not handle it at all, they hit a 3' wake or wave with NO bow lift or impact. The wave is simply split in half as you continue as if it never occured. If the wave is higher than the top of bow, a slight hesitation, green water on the deck and windshield. Any more than that height, driver is a idiot. These boats cut a hole thru all normal chop. NEVER do they lose their running attitude. The Scott-Paine 70' WW II PTB was designed and trimmed so that the entire hull would rise from the water, evenly. 39 tons 3300hp 44 knots--- beats offshore racers on eff. Why did the old timers do better than us with so little?

tom28571

01-09-2005, 02:04 PM

Sean,

Compared to what most mfgs are offering today, those look downright good. The ellipse window is better than the slash one and the pilothouse is not as nice as the rest of the boat but still, not a bad looking boat.

Rich,

It may be that many of the smaller deep v's like yours are just too heavy to give good performance. Everything about a deep V tends to make it heavy. Weight to keep the deep hull in the water for stability, bigger and heavier engine to get it going, more fuel to feed the bigger engine, etc, etc. It's a vicious circle.

I only have a little experience with the classic inboard runabouts but my memory is that they aren't too good in rough stuff either.

My only time to ride a PT boat was on one converted to a air rescue boat off Myrtle Beach, SC AFB in the late 40's. That was noisy, rough, wet and a lot of fun to a teenager.

CDBarry

01-09-2005, 03:11 PM

This is fairly well understood, at least for most planing powerboat hulls - The basic technique is computer simulations using Zarnick entering wedge theory, possibly modified by Vorus's methods.

See www.shipmotion.com for typical applications and results.

intrepid71

01-09-2005, 05:50 PM

OK, I'll type slowly.

The discussion started about far out designs like foilers and such in the attempt to make for easy riding speed in high "chop". A boat designed to be optimum in these conditions is very likely to be way less suitable in other conditions and speeds.

For instance: A 22 foot boat of even normal deep V of, say 26 degrees or so deadrise, is going to be tippy at the dock and a pig between about 6 and 20 knots. By pig I mean big wake, nose up, gas guzzling, hard steering and no fun to drive.

Those are valid criticisms of the deep-vee form. Of course almost all planing monohulls have a transition range between dispacement and planing, where the boat is struggling to get out of the trough of its own bow wave. With a deep-vee this transition range where it is a pig may last longer than with other hull forms.

A foiler is not going to be very good unless it is on foils at speed and a problem around docks to boot and very sensitive totrim and overloading.

The fully retractable hydrofoil I was proposing would eliminate some of those problems. Sensitivity to weight shifts and overloading are valid concerns however. The feedback system would have to be able to handle shifts and the operator would have to be careful about overloading.

A cat that is optmum on the waves is likely to not steer or maneuver really well at low speed and is sensitive to overloading.

I have read reviews of powercats and I have never heard of low speed manueverabilty as a problem. With twin engines widely spaced, I would think they would have an advantage in close quarters.

Some of these problems can be treated by sophisticated design and controls much like the computer "fly by wire" systems on modern aircraft that are inherently so unstable that a pilot cannot even fly them without the computer.

Wow, I wouldn't suggest going to that level. We are talking about a recreational boat, not an F-16. A fully submerged hydrofoil is the only boat I can think of that is inherently unstable. Some kind of mechanical or electrical feedback control system is needed to maintain level. That is the biggest reason I gave up on designing one. We are not talking fly-by-wire but it is still more than I want to get into.

That is what I meant, no more, no less. If there were any such boat design that did everything in excellent fashion, it would have been found by now and then designers would be out of work and we would have nothing to talk about.

Tom, I would agree with you that no single boat design is going to perform every function with excellence. You can't be all things to all people. Good boat designs work because they satisfy the needs of their intended niche. You wouldn't run an offshore center console in an inland lake bass fishing tornament, because the low freeboard and shallow-vee bass boats are lighter and faster and there is no need for the seakeeping that a deep-vee center console can offer. That doesn't mean that the deep-vee isn't a good boat, bass fishing on a lake just isn't the right job for it.

I still think there is a need out there for improved seakeeping in a small powerboat. If the design is going to be successful it is also going to have to be a reasonably good performer a variety of speeds, sea conditions and load conditions. It needs to be a well rounded boat. I think this is achievable. Perhaps it already has been achieved with some of the current powercats.

Richard Petersen

01-09-2005, 06:27 PM

Ther is NO NO difference between a bass boats purpose and a offshore fishing boat. Both are run wide open when the fish stop biting in one place and raced flat out to the next G P S. I am ONE ? of the nuts. Fresh and salt water. I have found out that the overpowered Chaparrel is one of the most comfortable Bass boats or offshore boats you would ever want ( full canvas is neat in August ).

intrepid71

01-09-2005, 07:38 PM

Richard Petersen

01-09-2005, 09:21 PM

I vacation along the St Lawrence River. Bass boats go out and stay out in 3 ' waves. Some do sink, winning is everything mental cases. What would that be similar to in the ocean? 10' ? Forget about the extremest nuts. Try to help me, a normal nut. :rolleyes:

tom28571

01-09-2005, 10:47 PM

I still think there is a need out there for improved seakeeping in a small powerboat. If the design is going to be successful it is also going to have to be a reasonably good performer a variety of speeds, sea conditions and load conditions. It needs to be a well rounded boat. I think this is achievable. Perhaps it already has been achieved with some of the current powercats.

I hope and believe that you are correct Intrepid. In fact, there are many boats now being built that are pretty good but that knowlege hasn't seemed to filter down to a lot of manufacturers that build some very unsatisfactory boats. A couple of local mfgs build boats that fit that category. I had a center console one myself that looked good to my untrained eye at the dealer. However when running at an angle into the wind, it would stick its sharp nose into the waves and try to throw the crew overboard as a result of bow steering. It also had that broad, don't run here, speed range. That experience started this sailboater on the path of trying to learn about powerboat design. I can't always predict the good ones but have learned something and especially things to avoid in the bad ones.

I expect that most of us here are somewhere on this same learning curve.

Richard Petersen

01-09-2005, 11:14 PM

Me to TOM.

tom28571

01-10-2005, 09:07 AM

OK Sh,

I get it. Your name is:

Urasmus B. Dragin :D

randy kahn

01-10-2005, 10:47 AM

intrepid71, in my opinion the glacier bay hull shape is the most outdated and sloppiest ride available domesticaly in a cat. (it rolls like a monohull with soft chines and has a tunnel slap that rattles your teeth and sneezes constantly)it still rides better than any similarly sized monohull hence the owners of these boats are happier than they would be in a monohull.The hull is based on australian small boat displcement sailboat hull design they abandoned for planing hull shapes well over a decade ago. the displacement hull in a powerboat is typically used on larger boats because of the horsepower requiements necassary to plane a large hull. look at a planing hull under 30'.....you mentioned what i like to call a 'shape changing 'hull and there are many ways to deliver variable operating characteristics by having a hull modify running surfaces while underway. the closest thing i have seen to your specific description is a small multipurpose coastal military surface craft in developement by lockheed martin. great potential but a bit pricey for recreational use at this time. once again my first choice for comfort and all around function is a planing catamaran for the size range you indicated. beware clever marketing and take a salty friend whose judgement you trust on a test ride in sloppy conditions and see for yourself. a salesman can pick the water and run a boat in such a way as to mask design shortcomings. you must 'box the compass' while running at speed and feel for yourself what a hull is capable of. good luck. Randy

Willallison

01-10-2005, 10:32 PM

tom28571

01-11-2005, 08:36 AM

Will,

That's very wise from one who thinks from the bottom up. :p Or, is it the other way round :?:

I think those most effective solutions were disqualified.

intrepid71

01-11-2005, 08:43 AM

A little late on the scene, but let that not disuade me...
Tom - I'm a little surprised to see that you've failed to mention the two most obvious solutions here (unless I've missed them of course...)
1. Buy a bigger boat
2. The most sensible one.... slow down.
.....

Of course a bigger boat, which in itself will be more expensive, creates a host of increased costs. More for docking, more for haul-out, more difficult or impossible to trailer, more for fuel, more for bottom paint, etc. Sure who wouldn't want a bigger boat...if you can afford it.

Regarding suggestion number 2 you can always slow down. Wouldn't it be nice if you didn't have to?

Richard Petersen

01-11-2005, 04:47 PM

We really do not have to.-------DIVE DIVE---- OOOOGAHHHH. :) :) :) :)

Willallison

01-11-2005, 05:30 PM

Richard Petersen

01-11-2005, 05:43 PM

No body, was allowed to watch us!!!!!! :eek:

Richard Petersen

01-11-2005, 05:49 PM

VSV is a blooming self righting enclosed CANOE! How long can it hold it's breath and keep its engines running before your eardrums burst? :mad:

intrepid71

01-11-2005, 07:56 PM

...well, yes it would be nice if we didn't have to slow down, but as Tom has said over and over, unless you're prepared to accept some pretty fundamental compromises in other areas, then it can't (with current technology) be done. Sure - there are boats that travel comfortably in rough water (take a look at this one for instance www.vsvboats.com ) but try doing anything else in them and they are generally complete dogs.

So the challenge is to build a small rough-water capable powerboat that does not suck in other areas. I'm not ready to concede that this can't be done with current technology. I am curious which characteristics are of particular concern. The following come to my mind:

1. Layout and functionality - a boat needs to have the space available for typical boating activities, like fishing. This rules out the VSV, where about 60 percent of its length is needs to be cambered deck.

2. Aesthetics - As the bumper sticker says "Life is Too Short To Own an Ugly Boat". This rules out many "out there" designs.

3. Draught - A small powerboat with a deep draft is about as useful as sh*t-flavored lolipop. This rules out fixed hydrofoils and HYSWAS.

4. Sensitivity to Weight Shifts - since people can make up a good portion of a loaded craft's weight, and people tend to move, we can't have a design that is very sensitive to weight shifts. This rules out most SWATH concepts.

5. I could keep going but I ran out of time.

Skippy

01-11-2005, 08:20 PM

4. Sensitivity to Weight Shifts - since people can make up a good portion of a loaded craft's weight, and people tend to move, we can't have a design that is very sensitive to weight shifts. This rules out most SWATH concepts.
That would favor a trimaran. Fuel tanks could be in the floats.

Richard Petersen

01-11-2005, 09:35 PM

Toot toot-- to the rescue! Higgins Landing craft. Great beach plank or casting platform-- adjustable diving board. Responsible drinking boat, if you can fall overboard you are not drunk- if you are drunk, you can't.Sounds like a good,fun, safe, stable, boat for all occasions. I will pick the gang up at 9. ;)

Willallison

01-11-2005, 09:39 PM

For a multihull to work effectively, the hulls must be long and narrow. Displacement cats need a minimum length:beam of 10:1 and many have much higher than that. True a planing cat can be wider, but then you start running into pounding problems.
So, for a trimaran with an LOA of 30ft, the main hull would need to be no wider than 3 ft. Not too good on the accomodation front. Yes you can use the space to some extent out to the ama's but, multi's like to be kept light, so really a trampoline would be best here. The there's the problem of trailerability. Ok, some tri's fold to go onto a trailer, but it all add's to the complexity and makes the launch / retrieval a long-winded affair. Plus they can be a bitch to tie up alongside a jetty.
Compromises, compromises......