1965 Dorsett Sea Hawk 18'6" Jet

Discussion in 'Powerboats' started by Lt. Holden, Aug 22, 2008.

  1. Lt. Holden
    Joined: Sep 2007
    Posts: 137
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    Location: Western Massachusetts

    Lt. Holden Senior Member

    Hi all,

    I am getting ready to dust off this old project of mine, originally completed in 1983. I used it for several years until the clutch broke and am now thinking what I want to do with it. The hull itself is in very good shape except for the starboard stern fin and the engine cover.

    You will note the unusual Hamilton jet pump to which I added a Navy Deadeye Missile fin as a skeg. The part that holds the skeg is stationary while the outer sleeve rotates and slides up and down for direction.

    I am thinking of finishing the engine cover with some nice veneer as well as the dash and gunwale recesses. Any suggestions for material and adhesives?

    I will follow up with some additional pics of the engine etc. The boat was originally powered by a Ford Industrial 200 c.i. straight six which I am told produced 100 h.p. (continuously rated). This sounds low to me especially for first generation jet pump. I don't want to go like a bat out of hell but would like a top speed of 40 knots or so.

    Attached Files:

    Last edited: Aug 22, 2008
  2. Lt. Holden
    Joined: Sep 2007
    Posts: 137
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    Location: Western Massachusetts

    Lt. Holden Senior Member

    More Pics as promised.

    The engine is a B&B 1974 Chevrolet 350 c.i. truck block built to Smokey Yunick's Marine Endurance specs with 1.96" valves for 300 h.p. @4000 r.p.m. It is simply too heavy and too much power (and gas consumption:( ) for my needs. I am looking around for a suitable re-power to save weight and gas. But I am hampered by a lack of knowledge of what the horsepower/r.p.m. should be.

    I have read that jets don't really require a lot of torque but like high r.p.m.; but the thought of watching a flow meter at 4000 r.p.m. makes me want to ralph. What about the possibility of running an over drive type unit; maybe 1:2?

    I really love the lines of the hull and topsides and I think she could be a real head-turner if I do my part. Any thoughts, comments, suggestions?

    Attached Files:

  3. Jango
    Joined: Aug 2005
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    Location: Mid Atlantic

    Jango Senior Enthusiast

    HP is a function of weight and speed as well as Hull design.
    In order to achieve 40 knots with a propeller driven craft, Assuming a total weight of 1600 lb w. fuel and passengers, would require 105 HP. Not sure how jets compare, but would think less effecient. I suspect many of the domestic as well as Asian 4 cyl. auto engines (140 - 160 hp) would do the job. Of course, they would need to be properly marinized.
  4. Lt. Holden
    Joined: Sep 2007
    Posts: 137
    Likes: 1, Points: 0, Legacy Rep: 20
    Location: Western Massachusetts

    Lt. Holden Senior Member

    Jango, any specific suggestions as to make and model? I had inquired here about Subaru and Mazda. The Mazda seems apealing due to its compact size, smoothness and high-rev capability but the marine conversions cost a sick amount of money and the fuel economy is questionable. The Subarus are available but with no (as far as I know) commercial conversion parts available it becomes a potentially very expensive lab experiment.
    I would be open to something funky like LNG steam turbine or even electric if it were financially doable. I run the Connecticut River (with trailer) from New Haven, CT to Brattleboro, VT with my home area being Springfield, MA. This leaves me 5 miles south to the breached lock at Enfield, Ct and about 12 miles north to Holyoke,MA. If I could come up with a relatively inexpensive Electric/LNG hybrid that could give me roughly 50 mile range at 35 knots I would seriously pursue it.

  5. Kris Akers
    Joined: Sep 2020
    Posts: 1
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    Location: Indiana

    Kris Akers New Member

    Curious question about your Seahawk. I have A 1965 Dorsett Seahawk with the Ford straight six. The passenger side component of the engine says “Dorsett Marine”. The piece has a crack and is spraying water out. I’m sure I could Weld it but thought if you swapped your engine, maybe you have that part handy or know someone/somewhere I could get one. I’m new to this boat and don’t know what that piece is called. I’m just trying to keep her in the water and away from a scrap pile. Any information is greatly appreciated.
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