My 32 foot powercat design for offshore fishing / day trips in the Gulf

Discussion in 'Boat Design' started by kengrome, Jan 1, 2010.

  1. kengrome
    Joined: Jul 2006
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    Location: Gulf Coast USA

    kengrome Senior Member

    Although I do not need the high speed for my own personal use, I think it makes sense to design and build this boat so that it can run at the same high speeds that many monohull pleasure craft can run in this part of the country. If I can design such a boat -- and also make it economical to run at reasonable speeds (I define reasonable as any speed up to about 25 knots) then I may have a unique boat that I can reproduce and sell commercially in the Gulf Coast region some day.

    I think the commercial potential for such a boat does exist, especially in the catamaran configuration which provides other desirable characteristics -- such as easy and practical beachability, excellent handling and docking performance with widely separated twin engines, a dramatic increase in stability at rest, and a 2-3x increase in usable floor space compared with monohulls of similar displacement.

    Having said this ...

    If I become convinced that 50 knot speeds are not that important to the local boaters then I can forego the high speed requirement and of course this would make my design challenge much less "challenging". But given the fact that the local boaters always seem to be looking for the fastest boat they can afford, demonstrating that this boat can reach 50 knots might be important to its commercial viability -- even if I never run my personal boat that fast.

    The goals for this design have little in common with yours, Masalai. I agree that you have done a great job of designing a boat for your purposes, but the boat I am designing has a very different purpose.

    I know it is difficult for most of the folks in this forum to consider the possibility that a boat might be nearly optimized for efficiency at 25 knots and at the same time be capable of 50 knots. And I may very well be wrong to focus on the Seaknife hullform for such a boat. But I have to start somewhere, so I started here.

    One more thing, I just want to thank everyone for all your comments so far. Your arguments to just forget about the high speed planing capability are clearly valid for a single purpose design. I just want to stay true to my original goals and try to come up with a hullform that serves two purposes if I can ... at least until I become convinced that it's not worth the effort.
  2. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    I am building this boat out of wood and lengthened to 31'
    The speed depending on horsepower can well exceed 50MPH. Just sending you this link for you own info. Go to customer pictures and look under Bearcat Cuddyto see a completed boat. Beam can be increased to 11' so says the Naval Architect.
  3. kengrome
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    kengrome Senior Member

    Thanks Rick, I find it very interesting!

    To me this suggests two things:

    1) The Seaknife hullform is not an efficient planing hullform. Even so, it still has some very desirable high speed performance characteristics, the most important being its ability to dramatically reduce vertical accelerations. This feature is the main reason I selected the Seaknife hullform in the first place, because even though it is not the most efficient hull at 20-25 knots the boat must still be safe and predictable and offer a smoother ride at 50 knots than other boats.

    2) The use of retractable "planing wings" during high speed operation might be a good way to achieve more efficient high speed planing on a Whio-type hull (I think Whio's efficiency is very much tied to its extreme light weight however, and this is not likely in my design).

    It is nearly always desirable for a boat to change trim as little as possible throughout its speed range, but I suspect that my current hull design will pitch up quite a bit.

    I agree. I think that a full width transom only offers an advantage in my design because it is an integral part of the Seaknife hullform, and this hull creates a soft ride at high speeds.


    I thought that using rocker to keep the stern above the waterline was an effective technique at higher speeds too. Thanks for this insight. It is important in this case because it means that if I insist upon having a transom I have no real reason to try to keep it out of the water when 80% of the time the boat will be driven at 20-25 knots.

    I think that if I go with a canoe stern I won't be trying to push the boat to 50 knots. To me, the use of a canoe stern is something I should consider only if I abandon my goal of 50 knots.
  4. erik818
    Joined: Feb 2007
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    erik818 Senior Member

    The Savitsky spreadsheet I'm using was meant for normal v-bottom planing hulls at speeds where the chines are dry. I believe that it calculates the dynamic lift well enough for the given trim angle for your long narrow hulls, but that's about it. The bottom area was a triangle 9 m long and 0.45 m wide.

    I think the power estimates are realistic. At 7 knots you are below "hull speed" and the two long narrow hulls shouldn't require much power even though the aft isn't optimal.

    My own "traditional Swedish Snipa" is a 7 m, 1.5 tons, displacement boat with a 7 hp diesel. At full throttle it will do 6 - 7 knots. The 2*1 kW predicted for a 2 tons 9 m power cat at 7 knots would correspond to something like 5 hp when propeller and transmission losses are considered.

    As I've already written, I'm using the Savitsky and Michell performance prediction methods outside the "definition envelopes" (don't know how to phrase that), so regard the results with caution.

    By the way, I think you are right to attempt a power cat design that has the potential for high speeds if this is what the market wants. Leisure boating is very much about dreams. The speed fanatic might dream about 50 knots and wants a boat that can achieve this, but at the end of the day I think he will usually travel at a more comfortable and economic speed.

  5. kengrome
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    kengrome Senior Member

    You are right on the money with this interpretation!

    I know that my friend seldom runs his boat at 50 knots even though he can. The fact is, he likes to tell people it can run that fast more than he actually does it. But he can do it, and he has done it numerous times, although usually not for long because even in relatively decent conditions someone ends up hurt because of the rough ride. Or if it's just him and me he will back those throttles down after a couple minutes and tell me that it really costs too much to run that fast for very long.

    I'm not the same kind of guy as him, but he seems to be typical of the market around here. He's into this macho image where bigger and faster is better. If he has 50 knot capability he can boast to his friends, and when he feels like showing off he can actually push those throttles full forward and give his friends (and/or himself) a high speed thrill for a while.

    But at the end of the day he typically runs at 30-40 when conditions are good, and even slower when waves and chop pick up a bit.

    I guess I want to design and build a boat that can "fulfill the dream" for the folks who think like my friend, while at the same time fulfilling my personal desire for an economical vessel that offers several advantages over the typical monohulls in the region -- all in the same boat.
  6. sabahcat
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    sabahcat Senior Member

    Is that dream still relevant in the usa?

    It used to be all

    But now?

    Fuel prices on the up, housing values dropped so no more using that as an ATM for easy credit, one has to wonder if there is really a market for a 50 knot gas guzzler
  7. TollyWally
    Joined: Mar 2005
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    TollyWally Senior Member

    "if there is really a market for a 50 knot gas guzzler"

    Not at the moment, but some of us learn slow! :)
  8. masalai
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    Location: cruising, Australia

    masalai masalai

  9. kengrome
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    kengrome Senior Member

    While I was still in the Philippines I thought the market for "gas guzzlers" had probably dried up in the USA too ... but it hasn't, not around here anyways.

    There is still a huge market for fast boats (gas guzzlers as you refer to them) all along the Gulf Coast, and I think this is never going to change. Pleasure boaters only have so much time on their days off to get out to their favorite fishing grounds, do their fishing, and get home before dark. This type of lifestyle demands fast boats when the desirable fishing locations are 50+ miles offshore.

    It seems that many or most of the people who can actually afford such fast boats have barely been hit by the current economic downturn. The depression has hit certain segments of the population of the USA very hard, but at the same time it has not bothered other segments in the least. So although it may seem from news reports that the whole USA is suffering, I can assure you that this is not true.

    Besides ...

    My goal is to create a boat that is more efficient at the speeds used most by the local boaters. If this design succeeds I can argue that this boat will save local boaters lots of money on fuel, and therefore they will not look at this new boat as a gas guzzler.

    And since this boat is a catamaran I can also point out the fact that it will:

    1- give them a nicer ride with its long skinny wave slicing hulls
    2- offer 2-3 times the deck space of their current monohulls
    3- provide a more stable and comfortable work/play platform
    4- easily operate from the beaches around here

    These features are obviously desirable. But desirability is no guarantee of commercial viability, thus if the concept never becomes commercial at least I will have the boat I think I should build -- even if I never run it at 50 knots.
  10. Chris Ostlind

    Chris Ostlind Previous Member


    You'll be paying for 50-knot structure and 50-knot engines. That weight is going to be hauled around everywhere you go.

    Those are not more efficient fulfillments considering the oft stated goals of actually driving this boat around at more reasonable speeds.

    Picture a 60's era land yacht with massive amounts of sheetmetal and a 400 cubic inch engine... all for making the run to the market for the week's groceries and getting to and from work. Conspicuous.

    In my opinion, this is not a commercially viable vessel with any kind of long lasting potential. Doing a national search of Craig's list classifieds will show just what kinds of boats are being shed by the recreational boaters of the USA in light of this recession. Huge numbers of heavy-engined recreational craft are being listed by the thousands, as everyday folks drop the pretense of being able to afford a $500 weekend on the water... for just the fuel. The existing manufacturers of boats of this type are either already bankrupt, or teetering dangerously on the precipice. The boat shops that used to sell this kind of vessel are also going away at alarming rates.

    The truth is, things are going to change from what they have been to a different way of approaching boating solutions. Fuel prices, as well as simple economic realities, are going to take us there, whether we like it or not.

    I truly like where you are going with the base concept of an efficient cat for recreation and fishing, but this 50 knot thing just does not fit with what I see happening across the country.
  11. sabahcat
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    sabahcat Senior Member

  12. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie


    I think if you want to compete in the commercial power boat market you are in for a lot of competition. Besides, I think speed boaters want a small pocket roket.

    I think you have a good idea, I have been working on something similar for a while already.

    Displacement hulls works better at lower speeds than planing hulls, too slender hulls will have problems of their own. The displacement hulls would give a more comfy ride in any case.

    I would rather sacrifice a bit of speed and have a hull that works from slow to fast than from fast to very fast. If you want the fastest, there is always someone with more money and more resources that will come up with something more rediculous.

    A 10m cat handles differently from a small power boat. That alone places it in a different class. You won't get the same nippy performance from it.

    I like the more safety, more space, more comfort, more economic that this setup has to offer over a power speed boat. It means my wife can go along as some friends. You can stay on the water all day and doesn't have to beach 20 times to refil on fuel.

    Any way, We did play with the friend's 12m cat. Everything was great, except an idiot designed the hulls. They are neither planing nor displacing but semi everything and semi nothing. Good for slow cruising only and not fuel or performance efficient.

    At early speed the water started spraying up the bow. If the hulls were displacment ones we would have been able to reach probably double the speed we achieved. If designed for planing the boat would have been even faster. Personally I would have liked to see decent displacement hulls.

    The conservative guy would fit small motors for economy, the hooligan is going to fit 200's just to be the fastest.

    I haven't read all the comments yet, but I saw some good advice from some of the guys already. Couldn't have done it better.
  13. alidesigner
    Joined: Nov 2006
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    alidesigner Senior Member

    Some simple risk v's reward questions

    How much will it cost to build?
    How much can you sell it for?
    How much profit will you make?
    How much will it cost to get a Naval Architect to design it properly?
    How much will you loose if it doesnt work?

    The answers which only you can give will tell you the best way to proceed.

    Oh and 1 more, have you ever been in a small boat doing 50 knots in a slight chop?

    (BTW no I'm not fishing for design work)
  14. guldam
    Joined: Feb 2010
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    Location: Vallejo, CA

    guldam Night Crew at Fishyfish

    I ride on a cat ferry 5 days a week on my commute from Vallejo to San Francisco. These are large and powerful boats but they won't do 50knts. They will do about 34 kts depending on current, wind, number of passengers and who's at the helm.

    They are not however planing hulls. But even in nasty conditions they are comfortable.


    Hey Kenneth, Did you ever put a motor in that Tolman Seabright? Launch any boats while still a builder in the Philippines?

  15. kengrome
    Joined: Jul 2006
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    kengrome Senior Member

    No, I ran out of time before returning to the USA.
    Several, but not the Tolman which is safely and securely sitting upside down in a barn in Cebu until I get back there to finish it some day.
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