Jersey Sea Skiff Performance?

Discussion in 'Powerboats' started by FAST FRED, Feb 18, 2007.

  1. FAST FRED
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    FAST FRED Senior Member

    I have been reading the Pocket Cruisers thread , and trolling the web and believe that the Jersey Sea Skiff hull under body has lots to admire.

    The DISTURBER ,by Atkin & Co, described in Jan 1960 Motor Boating , would skim over sand with no damage to the running gear , and was claimed to be a fine sea boat in rough waters.


    The Tolman Skiffs , seem to be a variation , but designed for outboard power.

    I wonder what this very useful hull shape " costs" in terms of running efficiency?

    The designer claimed it was far better (25%+) than a conventional hull and some Austrians with a similar "Power Glider" claimed low wake , good speed and modest fuel consumption.

    I'm almost finished with a scaled down interior for STROLLER ,to have her fit into a container (39 x 7.6 and under 9ft high fits).

    The cruising advantage of a large flat section so she can either take the ground overnight , or at least be easy to roll into a Sea Land box for transport is very desirable.

    With a "trailer" weight of 8000 to 10,000 lbs (no fuel or water) the DL should be low enough , and the BWL fine enough for cruising at SL 2.5 or 3.

    So the question is what fuel consumption penalty , over a "conventional" hull would this Jersey Sea Skiff bottom cost?

    The quest is for a boat that can cruise at better than 5nmpg at SL 3.

    Am I dreaming?

    FRED
     
  2. FAST FRED
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    FAST FRED Senior Member

    This is the article from Motor Boating that sparks the interest.

    FF
     

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  3. tom28571
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    tom28571 Senior Member

    Well Fred, Looks like no one is too interested in the Jersey Skiff just yet. This topic has been discussed several times on this and other forums. I think this hull form has a lot going for it. It's the same basic form as "Rescue Minor" that Robb White built. It should make a very efficient mid-speed cruiser that works well in shallow and deep water. I doubt that it is good for speeds much over 20mph but under that, it should work well. I've heard that the Jersey shore fishermen used the deep flat center section to allow launching off the beach over rollers, protect the propeller and keep weight low at the same time. Sounds like a good deal to me.
     
  4. kerosene
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    kerosene Senior Member

    Hey I find this very inetrresting - however with my limited knowledge I cannot provide any relevent input...

    I wonder how big you can go with this kind of hull. When I grow up and move to some place where one can buy more than one bedroom for 500k$ I want to build some sort of weekender - efficiency for me is a key issue.

    h
     
  5. Willallison
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    Willallison Senior Member

    Fred, Have you looked into any of Dave Gerr's boats? He has a number that are variations on the Jersey Sea Bright Skiff. I think he discusses them a bit in The Nature of Boats
     
  6. FAST FRED
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    FAST FRED Senior Member

    I have The Nature of Boats in my library , and was impressed with his design. But I don't think his will run over sandbars with the ease of the Atkin..

    20K would be a great speed , if it could be done on about 100hp , a modern engine would need about 4gph , giving a nice affordable 5 nmpg.

    Slowing to 14 or 16K should do even better, and of course "LRC get home" at 7K would barely move the fuel gage!

    FF
     
  7. SAQuestor
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    SAQuestor Senior Member

    Fred,

    Actually I think this whole concept could fit right in with the Pocket Cruiser thread and the now nearly extinct Option One thread.

    As a friend of mine has told me repeatedly, “What’s under the water is important – What’s above is just aesthetics.”

    Given that repeated admonition, let’s speculate a bit and see if this sparks a conversation.

    I want a boat that is transportable from coast to coast. Not necessarily trailerable to the local pond for an afternoon’s joy ride.

    That boat must be comfortable enough for extended trips – durations of 8 to 12 weeks. But like so many other folks that have a bit of gray in their hair (or lack very much on top:eek: ) comfort is a personal thing in that some folks might still like to tent camp and some folks want a four-star hotel. Me? I’d be happy with a dry warm cabin, a nice strong cup-o’-joe and a comfortable seat to watch the rain fall in June while back in some fjord in BC or Alaska. And enough vittles to be able to stay away from a town for a couple of weeks.

    But the boat should also be sea worthy enough that a bit of wave and wind blowing down one of the straits up north would not necessitate scurrying for an anchorage. (Not that I am advocating being stupid and ignoring worsening conditions.)

    Range? 300 to 400 miles at a reasonable speed?

    Speed? What’s reasonable? For some folks it’s 20+ knots. Others might be content at 7 knots. For me, reasonable falls into the 10-14 knot range.

    Economy? Were “I rich beyond the dreams of avarice” -- Edward Moore –- then I wouldn’t worry too much about building and fuel costs. But being an average computerized desk-jockey I do have to watch both the build cost and operational costs. I’ll address build cost below – but my spreadsheet suggests that if I can average about 5 MPG then the fuel costs will be in the range of .66¢ to .75¢ per mile. Of course fuel cost per gallon, speed and sea conditions will play a major role in the variability of this, but I did calculate very conservatively.

    Tom and I have corresponded some good bit about his Bluejacket designs. As you might know, Tom has a new 28’er is out in plan form and if I’m willing to take a bit less of the ‘comforts’ along, we both think that it’s just about a perfect boat for cruising a part of the Great Loop a couple of summers from now. Then heading to Alaska the following summer and then exploring south Florida in the winter – yada, yada and more yada.

    As we all know, Tom has written extensively about his BJ24 and the reasons for that design, its goals and actual accomplishments. Look in the Option 1 thread and/or do a search for tom28571.

    Tom has designed a full planing hull form that performs in a very remarkable manner. Full planing at low speed is a key characteristic. Because the BJ24 planes at a nearly flat angle of incidence, the wake – whether at 12mph or 22 mph is –compared to a deeper vee fiberglass production design – nearly non-existent. Please see the videos that Tom has so graciously given permission to put on youtube.


    Liz accelerating from slow to full speed - about 22 MPH
    .

    Liz accelerating from stop to full speed - about 22 MPH.

    Liz ‘cruzin’ - about 12 MPH.


    Liz passing by at full speed - about 22 MPH.


    Liz passing by at full speed #2 - about 22 MPH.



    There are several features on Tom’s design that all add up to an efficient – in terms of fuel usage per mile – boat. The shallow vee and chine flats have been discussed ad-infinitum elsewhere.

    As I believe most, if not all of us that are interested in boat design will agree, bottom loading is a vital key to securing economy and performance from a semi-displacement or full planing hull form.

    This is where I’m still struggling a bit – the amount of ‘stuff’ that I feel like I need to tote along when going away from civilization for a few weeks will degrade boat performance by increasing the bottom loading factor. Tom’s boats are designed with a BLF of about 18 lbs/sq.ft. at rest and increasing to the mid to high 20 lbs/sq.ft. on plane.

    Other folks that are quite knowledgeable concerning boat design stuff, and that I have faith in for not leading me astray, also suggest that this range of BLF numbers are in line with some of the more efficient semi-planing/semi-displacement hull forms that have been admired from afar, witness Whio.

    Take a stroll over to Tom’s website where he has a new treatise on planing hulls posted.

    Fred, if you’re not too set on taking lots of ‘stuff’ along, you might seriously consider Tom’s 28’er as a suitable candidate. Based on his experience with the 24’er I’d think that an honest 6 MPG would be easily obtainable and maybe the MPG would get in the area 8 under the right conditions. That 8 MPG would lower the calculated fuel operating costs mentioned above even further!

    I’ll not impinge on Tom’s intellectual property by posting any illustrations – I’ll leave than to Tom. But as I have told Tom privately – my schedule says I need to start building in about 18 months if I’m gonna have a boat ready for those long summers that are fast approaching, his 28’er is the most likely candidate that I have found to date that will allow me to tow the boat across the continent and taste the waters of various cruising grounds while being able to bring the boat home to my residence.

    Best,

    Leo
     
  8. charmc
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    charmc Senior Member

    "But the boat should also be sea worthy enough that a bit of wave and wind blowing down one of the straits up north would not necessitate scurrying for an anchorage."
    For several years I owned and cruised in a old Pacemaker 30', a bit bigger than you are speaking of, but a true Jersey sea skiff hull. The shallow v hull with a flat portion that you describe is more properly a Sea Bright skiff. The Jersey sea skiff had a fine, deep v entry, transitioning to a flat bottom aft, usually with round chines. Mine had a skeg, which protected the prop and rudder, and gave excellent directional stability in quartering and following seas. I did not build her, but I did do quite a bit of rebuilding, i.e. replacing planking that had rotted out over the years. While it was not easy, the work was "doable" by a definite amateur -- me.

    As for seaworthiness, over the years I was caught offshore in a sudden summer squall on more than one occasion, but never worried about her seakeeping abilities. On July 4, 1976, after months of restoration, I took my family up to NY Harbor for OPSAIL 76. On the way back south, an onshore wind and outgoing tide created steep 6-7' seas. That night, several owners of fiberglass boats in the 40-50' range talked about how nasty and difficult the seas had been, with some passengers becoming ill. Our experience was a gentle rocking horse motion after finding the right speed, about 14 knots, just enough to stay on plane. At one point I noticed it was pretty quiet in the cockpit.... every one of my passengers had fallen asleep.

    I found that, while it was possible to drive the hull to about 28 knots, that speed used a lot of fuel, and the hull would pound heavily in a chop. At 18-20 knots, however, fuel consumption was cut in half and she would knife through the waves.

    For the cruising, seakeeping, fuel economy, and trailerability mentioned, something in the 22-24' range might be very good. The Sea Bright skiff bottom would facilitate pushing over a flat surface, or on rollers (rollers were used to move the early Sea Bright skiffs, used as lifeboats, across wide stretches of beach sand). The boat shown in the videos is definitely an easy-planing, and probably very economical design. My only concern is seaworthiness. By seaworthy I am speaking of big ocean swells. If the boat will be mainly used in lake and inshore coastal waters, that design would do very well.

    I realize my descriptive terms are imprecise, and for that I apologize. I am not a marine engineer or NA; just a guy with 40+ years of experience operating small boats, sometimes (never by choice) in very rough waters. The challenge for boatbuilders in coastal New Jersey was always to build boats that could handle rough seas, but with a shallow draft and protection for the prop. 80% of the coastal estuary waters have a depth of less than
    4', and a good portion of those waters are 2-3' deep. So jersey-built boats have good prop protection...or else!
     
  9. FAST FRED
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    FAST FRED Senior Member

    Great to get hands on feedback from someone to confirm the sea worthyness of this hull configuration.

    Placing the boat on a trailer allows far larger range at low cost , as does the ability to container ship.

    The Dalmation Coast , The Inside Passage to Alaska , the Med , Turkey,South Pacific and other really interesting cruising grounds are easily and inexpensively available.

    Our use would be to cruise the an interesting area for 3 or 4 months in good weather , and ship her to the next years playground , safe and sound , away from sticky fingers in the Sea Land box.

    Eventually we would bring her home and in our dotage trailer her to the many landlocked lakes and rivers here in the USA.

    The 39 LOA will allow some extra goodies to be brought along with out killing performance. The biggest weight would be as on the old commuters , the drive package.
    As diesel IS required (from a previous post where responders discussed the difficulty in obtaining gas) and for shipping , the price seems to be an engine weight 1500lbs plus tranny .
    This is the range of genuine industrial engines , marinized that have NO electronic cam or injection , and no belt to drive a cam , as the auto conversions do.

    For an out of the way cruiser I must be able to repair anything , and replacing a cylinder head because a cam belt broke , requires spares beyond what is rationally aboard.This leaves out the Styer or Yannmar.

    Hopefully the LB ratio of such a slender vessel will allow the boat to operate in a very economical range , at good speed.

    FF
     
  10. FAST FRED
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    FAST FRED Senior Member

    I found that, while it was possible to drive the hull to about 28 knots, that speed used a lot of fuel, and the hull would pound heavily in a chop. At 18-20 knots, however, fuel consumption was cut in half and she would knife through the waves.

    When operating was there a HUMP or WALL in the boats performance?

    In other words did the boat accelerate smoothly , each addition of throttle, giving a similar increase in speed?

    Was there any point where LOTS of throttle was needed to get above a speed , and then normal operation?

    Or where no matter what throttle was added , thats all she would go?

    Thanks

    FF
     
  11. charmc
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    charmc Senior Member

    Fred,

    I posted a reply to you earlier today, saw it added to the thread, now it's gone....strange.

    OK, here goes again. There was a wall at the point of transition from displacement to plane speeds. Typical cruising scenario: Barely nudge the throttle for maneuvering away from the dock or anchorage area, a bit more in the channel, up to 7-8 knots. Stiil less than 1/4 throttle. To get on plane, apply 2/3 - 3/4 throttle; she'd plane in a few seconds. At that point she would accelerate rapidly without any more throttle, or I would throttle back to about 1/2 to maintain a comfortable and quiet cruise on plane of about 14-15 knots. Once I tried incremental throttle changes to get a feel for performance under all conditions. From 8 knots to 15, it took a lot more throttle to get more speed, with the bow up, stern down, and plowing along with ever larger waves at bow and stern.

    I believe top speed was limited mainly by the prop. At 28 knots, the engine was nowhere near the redline, but more throttle made no difference in engine or boat speed, so a prop with a bit less pitch might have yielded a few knots more speed, at the cost of a lot more fuel use. The prop we had got her on plane easily, even with a heavy passenger load, so I never thought of changing.

    Does this description answer your question, Fred?
     
  12. FAST FRED
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    FAST FRED Senior Member

    Delightfully answered! Thanks,

    I wonder if the boat DISTURBER with the tunnel would do as well.

    With such an unusual hull shape after the propeller will the usual speed prediction computer stuff actually work?

    FF
     
  13. charmc
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    charmc Senior Member

    Fred,

    After reading the details on Disturber and the other boats in the article, I'm certain that design will give excellent performance with shallow water protection. As for your question on performance predicting software.....the main thing is to be sure all the design parameters are consistent with yours. Remember "garbage in, garbage out"?

    That said, Penn Yan was successful for many years with their Tunnel drive, a similar concept. Although their tunnel was more rounded, I would guess there should be much similarity in performance curves. There should be plenty of data available on Penn Yan designs. Here's a typical P-Y tunnel drive.
     

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  14. FAST FRED
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    FAST FRED Senior Member

    The usual tunnel drive is really different from the DISTURBER concept.

    The usual tunnel is simply a grove in the hull that flairs out to accept the prop & rudder.

    The Atkin design has the box keel in front of the prop , with the prop working in the water that flows around the box into the inverted V that is aft.

    A look at the thumbnail (enlarged) will show the concept.

    I wonder if the various Navy's of the world have a figured "better" box shape for their underwater appendages?

    But then I'm not sure a Navy vessel will be running a SL of 3 , but there sure over 20K!

    FF
     

  15. Geoh
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    Geoh Junior Member

    Fred
    My cruising plans for next few years match yours BUT
    I just bought this 1980 26' allweather boat ...only 31 or so made because nobody (except me) apparently is willing to go this slow...Seems to be everything you want except the 10k to 14k speed... www.allweatherboats.com

    Geoh
     
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