Stern shape design for surface drive/stern drive

Discussion in 'Boat Design' started by Alik, Apr 17, 2006.

  1. Alik
    Joined: Jul 2003
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    Location: Thailand

    Alik Senior Member

    I wonder if someone knows good links/referenced on stern shape design for different drive types. Specially interested in how to combine sterndrive and surface drive options with same hull mold. Thanks in advance.
  2. dougfrolich
    Joined: Nov 2002
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    Location: San Francisco

    dougfrolich Senior Member

  3. Janamon
    Joined: May 2006
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    Location: Auckland

    Janamon Junior Member

    A good idea is to have the transom at 45 degrees. This assists the vessel greatly while going astern. You can visit for advice…….
  4. dereksireci
    Joined: Jun 2004
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    Location: South Carolina

    dereksireci Senior Member

    Transom angle

    I don't know about the transom angle of 45º. Going astern is important but concentrate more on what happens when you are going ahead.
    Check out the Arnesom site they have some nice pictures of a bunch of transoms. On one 38' high performance powerboat I worked on, the bottom was tweeked over and over intil we were happy with the performance and handling with Bravo drives. Long after the hull mold was made a customer ordered the boat and wanted Arneson drives. The handling characteristics of his boat were much different with that drive. Designing for both configurations can be tricky.

  5. Frosty

    Frosty Previous Member

    If you dont have a 45 degree transom you will not be able to go astern attall. Even though you are in reverse it is possible for the boat to still kreep forward. This can problem can be solved by making deflector plates to simulate a dummy transom of 45 degrees. Surface props also need lots of air, if you do not and you have a depression there at the transom this can cause cavitation. Swim platforms etc. I know it sounds crazy but!!!!. Surface props can be made to work well on all kinds of boats but they are not attall like a conventional prop.
  6. Frosty

    Frosty Previous Member

    It would appear that the above information was --disliked by some one and had a point deducted from my reputation. Come forward sir -dont be shy and tell me what it was that you thought to be ---well what ever. I will back up everything I said with a web site containing the relavant information. I myself have worked extensively on surface drives. Please, come forward I cant wait to hear what it was.
  7. E Hanson
    Joined: May 2006
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    Location: Vancouver BC

    E Hanson Junior Member

    A number of years ago I was involved with an R&D project that used a Seafury drive, 440 hp diesel, and a 45° transom. Here is the short list of what happened:

    1. slow speed manuvering was a bear. The boat reversed fine, just control and direction were lacking.
    2. The 45° transom reduced the bouancy aft.
    3. the boat heeled excesivly at speed. This tends to reduce the effectiveness of a deep v hull.
    4. The boat wanted to turn port, she was not too interested in turning starboard.
    5. to combat the heeling issue we added trim tabs. No easy feat on a 45° transom. It was easier to steer with the trrim tabs then the helm.

    eventually the project was scraped, and the drive was replaced with a Hamilton 292 jet. Thankfully the hull was aluminium.

    We had a laundry list as long as my arm at the end of the project. There were still allot of things that we needed to try to get this boat to run right, but the money managers said enogh was enough.
  8. Frosty

    Frosty Previous Member

    Mr Hanson There are a few things that I have spotted in your storey. First of all seafury is not a drive I would have chosen for a single instalation. Sea fury is not a drive I would have chosen for any installation. A shallower v might have helped with the single. If you look at the web site you will see from their gallery that most are twin installations. This gets around handling problem immediately. You will see that the rudder is just a blade at the rear of the prop wash. A better drive for a single would have been the levi drive with its full tunnel rudder. It is without doubt that cats are more suitable for surface props . And finally Ille bet you didnt get any help from Seafury did you?
    You didnt mention the size of the boat, and you say the boauncy aft was reduced,--it want any thing to do with the 440Hp engine .

  9. E Hanson
    Joined: May 2006
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    Location: Vancouver BC

    E Hanson Junior Member

    Sometimes there are projects where someone very high up tells you that the boat WILL be a single engine, deep V, and oh, by the way the Seafury drive for you to use has just been delivered. Such is life.

    The hull's LOA was fixed due to a design spec. The 45° transom reduced the water line. It also made the aft of the boat fell "soft". especially in a following sea.

    On the otherhand, the cool factor of that boat was undeniable. Picture a 9 meter RHIB, military gray, Ullman suspension seats, prototype handle bar steering, and a great big rooster tail. Ah....Good times...

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