Efficient Boat Plans with Carolina lines and Down-East Semi-Displacement hull??

Discussion in 'Boat Design' started by johnnythefish, May 25, 2016.

  1. johnnythefish
    Joined: May 2016
    Posts: 36
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: E.A.

    johnnythefish Junior Member

    I may be opening a can of worms here as I know Carolina boats have some pretty hardcore followers, but there is such a wealth and breath of knowledge on this forum that I would really appreciate some input.

    I have built two boats in the stitch and glue style; the larger is a 19 foot center console which I use a lot for big game fishing. In the last couple of years I have got into blue Marlin fishing in a big way and this means pulling lures at 7-9 kts.

    When we do this in my 19 foot planing hull, it just hates this speed and my gas consumption sky rockets; I get a huge prop wash and it just doesn't "feel right". The boat feels very seaworthy but it either likes planing or going real slow - this is not its speed.

    I have fished in a friends 23 foot Panga (we call them Yamaha canoes here) and they never seem to care whether they are at 5 or 10 kts; there is just a smooth increase in speed with power and gas burn really doesn't go up much. And the boat raises fish.

    However, a long skinny boat is much more unstable and not so comfortable to fish from - and as hard as I try to like them I just don't want to own a Panga.

    So what I am looking for is plans for a boat that is comfortable at 7-9kts; but can go a little faster when I want to go home. Even 15 kts would be fine. In a ideal world it would look like a Carolina Hull.

    The boat built here http://bandbyachtdesigns.com/project...r-shop/nad-28/ has to be one of the prettiest boats I have ever seen.

    I have read on various designer and builder websites about boats that are more efficient at these "intermediate speeds" and that do it without going the long skinny route.

    ...http://ellisboat.com/ellis-hull-design-philosophy/


    ...http://bateau.com/studyplans/NV23_study.php?prod=NV23

    And as such it always surprises me that most Sportfishing boats are built on pure planing hulls, when the truth is 60-90% of their life is spent pulling lures in this "no-mans land" 7-9 kts speed.

    Of course on a 72 foot Custom Carolina hull this may be close to hull speed, but for a small boat it is not. It has been pointed out to me that we are rather spoiled where I live, having a pretty decent blue marlin fishery within 7 miles of shore, where many places guys are running 40 miles or more - so speed is more important than economy anyways.

    So...

    Are there any designs out there that marry the "downeast" "efficient" type hull with the Carolina look above the water line?

    Or is this so called "efficiency" of hull shape over stated?

    Would I for example, get a relatively more efficient boat at 7-9kts if I simply had a longer planing hull that was operating closer to its hull speed? Say a 28 foot planing hull and not a 19 foot one. (Please not I said "relative" as I know a bigger boat weighs more and will these need more power)...
     
  2. gonzo
    Joined: Aug 2002
    Posts: 13,383
    Likes: 329, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Lobster boats have a round soft chine and almost flat stern. Carolina Sportfishemen have a hard chine and about 14 degrees deadrise at the stern. The only fuel efficient lobster boat designs are very old. The new ones are targeted at higher speed with large engines.
    Have you considered a power cat?
     
  3. johnnythefish
    Joined: May 2016
    Posts: 36
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: E.A.

    johnnythefish Junior Member

    I have considered a power cat - and that may also be on the cards one day as a much bigger boat - but I am looking to build something in the 23-28 foot monohull range at the moment.

    So I take it what was written on the Ellis boat link is mostly hype then? Would a similar sized and powered Carolina hull have a similar fuel burn?
     
  4. HJS
    Joined: Nov 2008
    Posts: 333
    Likes: 44, Points: 28, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    The attached file displays a boat bottom that is effective over the entire speed range. The solution is a bottom with double chines. It combines the good properties of the round-bottomed boat with the V-bottom boat.

    js
     

    Attached Files:

  5. tom28571
    Joined: Dec 2001
    Posts: 2,469
    Likes: 113, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    It is inescapable that 7 to 9 knots is a terrible speed for smooth running in the size range you are interested in. That comprises the main part of what is known as the "hump" speed that most hulls are not good at. To run at that speed requires either a long lean hull or a decently flat bottom (flat or moderate V aft with straight buttocks) with both proper balance and light weight. Many of the prospective hulls meet some of those requirements but fail on the light weight issue and thus will tend to stick their bow up in the hump range.

    It is very difficult to have a deep V hull meet these requirements. The very nature of a deep V requires higher weight to meet stability needs. Some adherents of a deep V dispute that but I stick by it and eliminate that style as a possibility.

    Some V hulls help themselves by having trim tabs on the transom. These will help get the boat through the hump by doing two things. Preventing stern squat which makes big, high resistance, waves and lengthening the longitudinal waterplane which increases both hull speed and reduces the bottom loading. That last bit is apparently little appreciated by many builder and designers or they would not make their boats so heavy. By bottom loading, I mean the pounds per square unit of area of the hull in contact with the water. Trim tabs have their own price in needing more power to get on plane than a hull that does not need them but they can help some existing boats.

    Lighter weight boats tend to ride rougher than heavy ones and that is part of the compromise that any designer faces in mating a design to its goals.

    With a reasonable set of goals, all is not lost though. By reasonable is meant a balance of efficiency, accommodation, riding ease, speed and power requirements. That is a limited list and there are other goals that some individuals might consider important.

    In my own case with my own set of goals I designed some boats that move through the "hull speed" hump with the operator being unaware of its existence. If you look at the photo sequence of speeds here, notice that the transom never sinks at all (zero, none) from idle to top planing speed. The boot top is visible above the waterline at all speeds and only the bow rises but never more than 3 degrees which occurs at top speed rather than in the "hump" where most would expect it to be. Lower bottom loading means less wavemaking and a longer waterline means a bit higher skin friction resistance. Higher skin friction reduces top speed but not by much and I willingly accept the small loss in speed for the advantages. These boats were designed from a different perspective than the usual one. When people wanted a boat to run in the teens, they have invariably started with a displacement hull and made it faster. I started with an opposite view and took a planing hull and made it slower. This is more important than it might seem at first look.

    http://bluejacketboats.com/

    You may need to blow up the top speed photo but the boot top is there hiding behind the water splash. Bluejackets will not suit everyone or every situation but they do provide a good balance for the needs of many and handle rough water pretty well.
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 5,987
    Likes: 325, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Exactly.

    No matter what shape you try to make the hull, you're at the worse location on the resistance curve in relation to the length.
     
  7. abcdefg
    Joined: Mar 2011
    Posts: 38
    Likes: 3, Points: 0, Legacy Rep: 46
    Location: near the water

    abcdefg Junior Member

  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,511
    Likes: 243, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'd rather fish for something you can eat, and handling large marlin around small boats is dangerous. Try towing some rigged baits (bonito etc) at 4 knots or so, seems to be a lost art to use real bait ! I have caught marlin, and many different gamefish, on trolled bluefish (called "tailor" here). They "swim" well once you get the hang of rigging them. 3-4 knots gives them a good action.
     
  9. johnnythefish
    Joined: May 2016
    Posts: 36
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: E.A.

    johnnythefish Junior Member

    Thanks for all the responses - firstly to Mr Efficiency - we have not forgotten the "lost art" of live baiting and do an awful lot of it for Black Marlin which we get closer in and in shallower water near structure where it is easy to catch the bait; unfortunately for blue marlin we only get them out in the deeper water with little structure to concentrate them. Here, you very rarely can consistently catch bait - and as such covering large areas of water with lures becomes the only other sensible option. If I could live bait for Blues, I would.

    To abcdefg - the Brett Murrie design is a nice boat - but I don't see anything remarkable in its design or performance that it would led me to believe it will be the solution to my problem.

    As I said before, everything keeps pointing towards a panga in terms of efficiency for what I want to use the boat for, and it is no doubt why this style has become the choice of artisanal fisherman the world over, but I don't want to invest the time and effort in a build that I just don't like the looks of!!

    To HJS - thanks for that info - I will have a read through the PDF and try and educate myself...

    To Tom - in my quest for the perfect boat, I do now remember coming across your website and thinking "wow - I like the sound of this"... better still is the fact that there are some boats built in your style that means there are some real world figures... so a couple of questions...

    1) Do you think your boats would be happy far offshore? Operating as a sport fishing boat?

    2) Do you have some "real numbers" for fuel burn for some of these boats "trolling" at 8kts?

    3) Could the plans be modified to be built as a Centre Console?
     
  10. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,511
    Likes: 243, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    To hell with going wide in a panga. You lose a margin of safety in a narrow-gutted boat like that, OK maybe 99% of the time, it is the 1% that poses the problem. I know little about blue marlin, but I'd suspect trolling feather lures while on the way to the grounds should raise small tunas for bait ( 20 knots they catch the lure easily), so you don't need to pull lures all the time, and can troll live or dead baits at hull speed. I have always found in relatively heavily fished areas, the live baits or trolled dead bait, outfished lures. But your 8-9 knots may be giving you the advantage of covering more ground, increasing the strikes per hour.
     
  11. abcdefg
    Joined: Mar 2011
    Posts: 38
    Likes: 3, Points: 0, Legacy Rep: 46
    Location: near the water

    abcdefg Junior Member

    Johnny,

    That boat may look similar to many out there but it is not. I had a run on it and it ran very differently to any number of deep V boats. Being relatively narrow, low deadrise and simple (read light) pushes the boat in the right direction...

    It felt like a big surfboard getting on the plane. No real hole.
     
  12. johnnythefish
    Joined: May 2016
    Posts: 36
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: E.A.

    johnnythefish Junior Member

    abcdefg - forgive my assumptions - I don't know enough about hull design to see where one differs from the other - but I really appreciate your inout and real world examples are better than theory in my opinion. If you have been on one, do you know what sort of fuel burn it gets at 8 kts?
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,511
    Likes: 243, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    That boat would worry me in the rough, you would cop a flogging on less than calm days, imo. Nothing will happily go 8 knots in that size range of a monohull, you are left looking for the least worst. But the boat has to shape up as a conveyance out and back, as well as the trolling.
     
  14. abcdefg
    Joined: Mar 2011
    Posts: 38
    Likes: 3, Points: 0, Legacy Rep: 46
    Location: near the water

    abcdefg Junior Member

    Sorry don't have that info. Could say more than a panga, but far less than a deep V.

    Everything is a compromise....
     

  15. HJS
    Joined: Nov 2008
    Posts: 333
    Likes: 44, Points: 28, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    The boats I work with usually have a slenderness ratio, L / V^0,33, around 5.0 or slimmer. This in itself creates low resistance over the entire speed and no noticeable hump. Next to this, the bottom deadrise, the bottom width and the total center of gravity is optimized for smoothest motion in waves. If the boat should only to go in the semi-planing speed, you also have to calculate the transom area and its depth.

    Calculate, don't guess!

    That's what I demonstrated with the boats with double chines.

    JS
     

    Attached Files:

Loading...
Similar Threads
  1. mecmec
    Replies:
    4
    Views:
    4,908
  2. highamperage
    Replies:
    18
    Views:
    4,680
  3. mental_boy
    Replies:
    164
    Views:
    25,265
  4. Cutimo
    Replies:
    22
    Views:
    5,042
  5. Jeremy Harris
    Replies:
    509
    Views:
    254,424
  6. Chuck Losness
    Replies:
    46
    Views:
    19,578
  7. 07MAM
    Replies:
    18
    Views:
    1,518
  8. johnnythefish
    Replies:
    34
    Views:
    3,946
  9. xichyu
    Replies:
    22
    Views:
    2,140
  10. xichyu
    Replies:
    7
    Views:
    1,230
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.