Old design, modern power?

Discussion in 'Boat Design' started by graywolf, Aug 7, 2017.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Depending where you intend to be using the boat, the benefit of having an old design ( usually not rough-water friendly at higher speed ) with modern power that can produce more speed out of it, is questionable. Deep vees really only came into vogue as power plants got lighter and more powerful, designs reflect the power options of the day, and mixing them is of doubtful wisdom.
     
  2. graywolf
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    graywolf Junior Member

    All sea skiffs, as far as I know, are semi-displacement, or rather semi-planing boats, but 30-35mph is entirely possible (because the boats actually did that). Tunnel drive boats are really sensitive to having everything just right, so dealing with Little Water may be beyond my understanding. But, I am not as ignorant as you seem to think. My interest was not specifically in Little Water, but in what had to be taken into consideration when doubling, or more, the power of an old design.

    And, while I do have a feeling that enough power would push a boat like Little Water right over the hump, I do not know that for sure and can not afford to build one just to find out.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    There is really not much boat in the water, right aft, with "Little Water", but compensates with the pronounced hook, which is no doubt amplified by the propwash also acting on the hook. The shape of the hull excluding the aft part, is very much that of a semi-displacement boat, with the maximum waterline beam well aft. That boat could become rather unstable if it could be driven to 30 mph, as it rose on that wide flat along the centre. The design allows shallow draft, very good prop protection, level when stranded, but not high speed. It is optimized for, and built around, low power, by todays standards. It is really a 15 mph cruise boat. Something that is a rarity in small motor boats. A 30 mph boat needs a bottom with straight or near straight buttocks aft, this boat does not have that.
     
  4. graywolf
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    graywolf Junior Member

    Mr Efficency, have you ever run a sea skiff type boat?

    Deep V hulls were developed for ocean racing, designed to blast through chop with little more than the keel in the water. They are a long way from being the ultimate hull forum for anything else. For sportfishing, up to about 50 miles, offshore the sea skiff was/is about the best hull form. Many claim the sound of the hull moving through the water actually attacks fish. The big sportfishers (35-40 footers) actually ran out to Bermuda from New Jersey.

    The Lymon's were built in Ohio mainly for use on Lake Erie. Lake Erie is interesting because it is about 200 miles long aligned with the wind and averages about 6 feet deep. Needless to say when there is a blow it gets kind of rough. Sea skiffs are very seaworthy boats. But no, they were not intended to run 50 knots in those conditions, more like 18.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I have run a few kinds of boats, and whilst deep vees are not ideal fishing boats, many people are prepared to trade that off to lessen bone-jarring ride characteristics. Especially if it is a day excursion with a long round trip, people want to cruise at 20 knots in average conditions, where it is not too rough to be out fishing, anyway. 20 knots cruise will find a lot of shallower veed boats out, in that situation. They might have to back off to 15 knots, and that cuts into time that can be spent fishing. It is horses for courses, but over-powering old designs that are intended for more modest speeds, and only being able to use that power on odd occasions when the water is flat, does not make a lot of sense, especially as you may have increased the lowest speed the boat can hold a clean plane, by installing heavier engines. By that reckoning, a 350 CID inboard in a moderate vee fishing skiff, is probably not an ideal match.
     
    Last edited: Aug 10, 2017
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    No, those would be planing boats, look at the buttock lines aft, that tells the story. They don't have to be dead straight, but if they have much "rocker", the boat will be porpoising, typically, if it manages to get over the planing hump.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Your assumptions about sea skiffs being semi displacement are incorrect. It's a true full plane mode hull form. I used to have a 1960, 28' Chris Craft Sea Skiff, with the origional 185 HP, 283 still in her. She would run in the mid 30's easily. This is well past semi displacement speeds, by any definition. That Chris need to make 14 MPH to be considered in a full plane regime, doing well over double this, well . . . Essentially a sea skiff is a warped bottom or double wedge design if you will.

    A 20' - 24' sea skiff design with glued lapstrake construction wouldn't need laminated ribs, just some furniture and maybe a bulkhead or two. The Sea Skiff design is pretty antiquated and there's much better designs that certainly could be made to look like a Sea Skiff (or whatever), just with a more modern approuch to the hull form.

    As to what needs to be done to accommodate a new engine in an older design, well nothing really. An LS-1 developing 250 HP will work just as well as a first gen small block, developing the same HP.

    Chris Craft, Lyman and the others didn't change their hull forms when moving from flatheads to overhead valve engines. Only the propulsion details changed. They knew what power they needed and installed what was appropriate.

    If I was to design and build a new Sea Skiff hull form, it would be a monohedron design, with modest deadrise (10 - 12 degrees) to maintain the chairture of the boat's qualities. This would require a little more power for the same top speed, but the ride would be softer, she'd handle and trim out better. Most of the warped bottom skiffs had 0 to 6 or 7 degrees of deadrise at the transom. This permitted them to get up on plane fast with modest power, but lacked rough water ability and comfort in a chop.
     
  8. graywolf
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    graywolf Junior Member

    The certainly changed their design around that time. Both companies went from buff bows and tumble home sterns to widely flared on both ends.
    [​IMG]

    [​IMG]

    First boat is a mid-50's Chris Craft Sea Skiff, second is early-60's. In the 70's the flare was even more pronounced. Just marketing, or did it have something to do with the more powerful engines? I always assumed just marketing.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Styling changes are a natural progression, mostly marketing team and now focus group motivated. The hulls where classic warped bottoms, though each manufacture did eventually take "liberties" with the traditional seas skiff form. In their defence, much of this was to address concerns and ride comfort. Lyman for example prefered the deeper forefoot and finer entry approuch to the hull form, which made them about the best riding of these old classics, while Chris Craft was actively racing them so, lightening the forefoot and transitioning to a faster aft wedge, for better acceleration was employed, of course at ride comfort loses. A group of old fat guys, sat around a table and discussed what was necessary in their next new model, eventually settling on the priorities of the new SOR, for that design.
     

  10. ned L
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    ned L Junior Member

    Sort of an interesting thread that I would be interested in joining in, but there is so much cross information and so many generalizations that It would take a good while to unwind it all.
    PAR has a good handle on things (but you know that).
    The picture of the tough condition 17 ft skiff that Graywolf posted was built by Harold Jeralomon in Monmouth Beach NJ about 1920. I took that picture a year or so before I added her to my collection (yes, that is now my boat).
    There were some comments on the rum runners here. The early ones were boxed and rolled garboard keel fishing skiffs capable of maybe 12-15 knots. As things became more serious builders such as Koefod of Keyport began building the large fast rum runners with triple Liberty aircraft engines. These boats had flat sea skiff bottoms and not boxed or rolled garboard keels.
    Boxed or rolled garboard bottoms can be built with or without a hook. Some builders (such as King of Highlands) built with a noticeable hook to get up on top sooner , and to get up on top while carrying more lobster pots.
    Yes, diesel engines were installed in boats of all types. Charlie Hankins of Lavalette built a good number of nice little 24ft boxed garboard keel shelter cabin cruisers with a 4 Cyl Lehman Ford diesels, They cruised very nicely at 12 knots and did 17 knots wide open.
    The 16 ft speed skiffs actually are quite capable little boats.
    The boats of the N. Jersey shore (Morgan to Neptune) were for the most part developmental builders, and did not work from "designs". Harry Zobel being one exception, and did have William Atkin do some design work for him.
    Banfield boat works (~1911 to 1935) advertised their boats were capable of running in the low '30's, and had boxed garboard or rolled garboard keels (not sure which at this point,.. tending to think boxed keels). They built something like 3000 boats.

    If anyone is interested in reading more about these boats and their history you might google "Jersey shore old school sport fishermen" and look at a thread on THT.
     
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