Downeast hull design

Discussion in 'Boat Design' started by Marc78, May 17, 2006.

  1. dobsong
    Joined: May 2009
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    Location: Australia

    dobsong Junior Member

    Replacement for Snark

    Tad,
    Thanks for picking up my mistake about the output curves. So in theory with the 6CH-HTE3 14 knots is @ 2260 rpm so its sounding like 15 knots will be the top speed if we take the engine to its maximum output of 190 hp @ 2600. I was hoping for something closer to 18 knots as a maximum.

    The 6CH series weigh in @ 675 – 730 Kgs dry. Maybe we should be looking at the 6CH-DTE3 which is rated @ 210 hp @ 2550 rpm or the 6CH-UTE which is rated @ 255 hp @ 2550 rpm. Or do you have another engine you would like to suggest that you think would be a better match to my requirements?

    You stepped around providing suggestions for achieving the “target” 1 litre per nm @ 12 knots and 1.3 litres per nm @ 14 knots (though from the figures you provide we are close). Do you have any suggestions on how this design could be ‘improved’ to achieve (or exceed) these targets?

    I’m guessing fuel is about a Kg a litre so the 800 litres will be approx 800 Kgs. For 400 litres of water is another 400 Kgs. So I’m guessing the all up weight of fuel, engine, batteries (300 kg), toilet etc would be have to be getting close to 3,000 kgs, not sure what the hull and fitout would be….. I’m wondering if there is much weight to be saved by the choice of construction materials (hence my previous question on yellow cedar planking). I take your point about making her too light and therefore having a too quick motion – again I assume having the big solid keel will help to dampen this….. as will keeping weight low and not having too much “air height”… What are your thoughts or suggestions?

    One of the things I really liked about the White Pine design was the access door from the helm. Do you think that could be provided in “my” boat? Do we leave the ‘bridge deck’ open to the aft cockpit or closed? I’ve seen a boat with a nifty setup with a central door and drop down windows on each side. (that boat had a 14-15 beam so I’m not sure it would work with a narrower beam?. What are your thoughts?

    Also in and around the engine compartment and workspace for servicing inspecting etc is important. I am assuming (yes I know ***/u/me) that there would be a largish (?) hatch above the engine and this combined with the ‘headroom/crawl space would mean easy access. Do you agree?

    Sorry about loading this up with questions but I do think you are getting close to a design outline that will suit what I want.

    I look forward to your response.

    Regards, Graeme
     
  2. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    This hull with a full size skeg can handle most all waters and can be lengthened to 36' W/O any problems. You design your own cabin which is what I'm doing. You will need a kicker engine for safety or go with dual inboards. Just a thought for you. This is built strong and you could use your white pine in cold molding.https://www.boatdesigns.com/products.asp?dept=729
     
  3. dobsong
    Joined: May 2009
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    Location: Australia

    dobsong Junior Member

    Hmmmm

    Sorry Rasorinc,
    Not a hull desgn that appeals. Why would I need a "kicker" engine or inefficient twins! Down my way (Bass Strait, Southern Ocean, Tasman Sea) a very large percentage of the commercial fishing fleet just have the one engine in their boats.

    The main problem regular boat users seem to encounter (apart from rough weather) is all the crap in the water fouling props. Most engine problems seem to be with boats that are from water in fuel, or rarely used (one survey her showed 80% of marina berthed boats do less than 5 trips a year) or not well maintained or a combination of all of these.

    I am totally happy with my decision to use just one engine. I also venture into a shallow areas so grounding does happen hence my desire for a good solid keel that protects the prop (a friend of mine, with a twin engined shaft drive and no skeg, touched the bottom and ended up with a huge bill to have his props straightened and balanced... about a third of the cost was getting the boat out of the water and storage on hard standing while waiting for the prop guys to do their thing. I was with him when it happened and also touched the bottom but because of my keel all I got was red faced.

    I also wonder about adding weight, especially up high, to designs. Recently a 36' boat tipped over of the Tasmanian coast and from the coroners report it seems most likely because of a generator that had been bolted to the cabin roof and a 'tower' built above the cabin. So i'd want a cabin only to be there if that was the way it was designed!

    Regards, Graeme
     
  4. Tanton
    Joined: Nov 2003
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    Location: Newport RI

    Tanton Senior Member

    29'.Downeast hull. Skeg. Not a Madison Ave. speak.
     

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  5. ned L
    Joined: Nov 2008
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    Location: N.E. Connecticut

    ned L Junior Member

    dobsong, very nice boat your "Snark". It looks like her designer may have been influenced by the typical "Jersey sea skiff" of the New Jersey shore (east coast U.S.).

    [​IMG]


    1951, 30' Ulricsen skiff - White cedar on oak
    [​IMG]
     
  6. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    Please understand that we're just talking generalities here....I might undertake design refinement calculations for the edification of this forum....or I might not. The physics are fairly simple....make the boat smaller and she will use less fuel. My first figures were based on traditional wooden construction and a displacement of 17,000 pounds. Going slightly smaller, (say 40' by 9') and to foam cored construction with a modern engine can drop this by 3-4000 pounds, easily achieving your desired goals. Alternatively a slightly more powerful engine and careful weight control in design and build may do it as well. Your targets are well within the margin of error of my ballpark estimates.

    Also I try to keep numbers presented erring on the conservative side.

    The Cummins 6BT5.9-M produces 180 Hp at 2500 RPM and weighs 509 kgs.

    A great deal of weight can be saved by careful choice of materials and good engineering. The builder will play a big role in this, if he's weight conscious throughout the build, and drag conscious in the detailing, it can make a huge difference. That and an owner who is careful about additional weight on the boat over time.

    A canvas back wall will be light and easily removed. The sliding helm door is a popular feature for shorthanded use, there's no reason not to include it.

    The reason for keeping the deckhouse somewhat clear of furniture is to have big sole hatches for engine access. As there's about 3' of depth to the engine room, one should be able to stand up on either side of the engine.
     
  7. dobsong
    Joined: May 2009
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    Location: Australia

    dobsong Junior Member

    Are we just stuffing around?

    Tad,
    I'm serious about getting a design finalised and then getting the boat built. You stated "....might undertake design refinement calculations for the edification of this forum....or I might not"

    I assumed that when you got my email (sent to you on 18th May) you would have understood that I am serious and looking for a designer to develop plans for what I want. I assumed that this would mean a commercial relationship. Guess the old ***/u/me principle may be at play!

    So to make myself absolutly clear! I am looking for a designer to assist in the design and construction of a 38 - 42 boat in line with the requirements I have been providing. I fully understand that once I find that designer and we reach agreement about the design "concept" there will need to be a commercial arrangement.

    What I am now wondering is.... Are you that designer?

    Let me know
     
  8. Tanton
    Joined: Nov 2003
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    Location: Newport RI

    Tanton Senior Member

    38' Lobster boat. H-P. from 120 to 650.
     

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  9. dobsong
    Joined: May 2009
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    Location: Australia

    dobsong Junior Member

    Thanks for the picture Ned L.

    Hmmm it seems Halverson & Sons did a bit of copying.....
     
  10. Boston

    Boston Previous Member

    not a bad guess Tad
    the actual displacement weight of the 57 flat top was 21 tons
    heavy on the finish and light on the scantlings
    Thats why if you read the diagonal planking thread you will see that I was seeking ways to stiffen the structure and lighten the finish while maintaining the skeleton rather than forsaking it as in a purely cold molded type hull.
    I increased the rib spacing, obviously the ribs themselves and went with double diagonal planking and a plywood sub floor under the deck rather than the original ceder carvel planking and deck. Basically I made the frame a lot beefier and lightened up on the interior finish. I also was thinking of framing the canopy and going with a cloth covering rather than a roof deck.
    I wanted to showcase the skeleton anyway, loosing some of the interior wall treatments and the heavy finish features in certain areas in order that the structural components could be strengthened for open water.

    so the down east hull as a 60' will yield a speed of 15 knots at 300 hp in flat calm water no wind or currents with a cruise of 9 knots at 44 hp

    thats an improvement over the purely displacement hull at the higher end and virtually identical at the lower which is exactly what I was hoping for
    Hmmmmm
    gives me food for thought
    thanks
    B
     
  11. Kimbo
    Joined: Jun 2009
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    Location: Richmond

    Kimbo Junior Member

    MMD,
    I'd like to get some information on your 26 foot Cape Island. I joined the site in order to PM you, but I understand I have to make 5 posts to have PM access.

    Can I ask you to PM me with your preferred contact information?

    Dave
     
  12. Kimbo
    Joined: Jun 2009
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    Location: Richmond

    Kimbo Junior Member

    MMD,
    Can I ask you to PM me about your Cape Island design? I'd like to discuss with you in more detail off-line.


    Dave
     
    Last edited: Jun 19, 2009
  13. dobsong
    Joined: May 2009
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    Location: Australia

    dobsong Junior Member

    A 39' "downeast" influenced design - Feedback Request

    I'm part the way through getting a boat designed and was thinking I sould get some feedback from others before we finalise the design and begin construction.... So here goes!

    She is for open water coastal cruising, 11.9 metres LOA, 11.7 metres DWL, Beam is 3.3 metres and draft is 1.1 metres. Displacement is anticipated to be 6,100Kgs fueled and loaded for cruising. She has a rounded "ducktail" stern

    She will be powered by a 315hp Yanmar and we are expecting a cruise of 14-15 knots and a top of 19-20 knots. She is to be built using Celery Top Pine, a wonderfully tough timber from Tasmania.

    These are the profile and layout drawings.


    Revised Profile 18 August.jpg

    Layout 14 July.jpg
     
  14. MartinV
    Joined: Jul 2011
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    Location: Netherlands

    MartinV Junior Member

    New here and requesting some additional info

    Hello all,

    My name is Martin and I live in the Netherlands. I am starting to get more and more interested in boats and in the near future would like to build or buy one. As, I guess, many people I am attracted to lobster boats, both for their look and ruggedness.
    For now, I would like start of with building a model of a lobster boat. I saw the drawings of the "White Pine" and thought it a nice boat to start with. However, the resolution is just to low to make out the values along the (iso)lines of the hull. Can anyone supply me with the figures or a slighty higher resolution drawing?

    Much obliged,

    Martin
     

  15. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    For those of you who really want to get into the history of the true lobsterboat hull development , Wooden Boat did an excellent article some years and years ago. If my old memory serves me well the hull form was derived from a fishing craft called a Novi. Since then it has been modified and misnamed into a hundred different shapes and sizes. However if you refer back to the origional Novi hull form and it matches closely I see no harm in the Lobster yacht claimiture other than that, call it what it is, a modified Novi-A Downeaster, A Cape Islander, A Northumberland, and so on. Example a Labrador is just a stage name for The St. John"s Water dog, I guess one could truley call it a "Modified" St. John"s Water Dog -- :) Geo.
     
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