Savage Scout Hull Extension

Discussion in 'Boat Design' started by savagescout, Jun 6, 2009.

  1. savagescout
    Joined: Jun 2009
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    Location: australia

    savagescout Junior Member

    Hello There,

    I am a first time poster on this forum and about to embark on a large restoration of an old Australian built Savage 23 foot cabin cruiser. (as per below)

    [​IMG]

    The boat currently has a v8 mercruiser in it which is dead and I have bought a late model turbo diesel (220hp mercruiser) which I am planning to install in its place. The diesel should be a nice motor to install in the boat but the biggest issue is it is 500mm longer than the current engine.

    After some soul searching in the boat, I became unhappy with the deck space in the aft cockpit and it occurred to me that maybe I could extend the hull. I have decided that installing an additional 3 feet would make a great boat.

    I would take a mould of the aft section of the hull and then cut the boat approximately 1-2 feet from the transom and then glass in the 3 foot extension. Obviously I will structurally reinforce the hull appropriately.

    Below is a photoshopped image of what I want the hull to look like:

    [​IMG]

    The hull has a beam of 8 feet and is 23 long currently. The deadrise is approximately 16 degrees.

    My question is:

    How do you think the additional 3 feet will affect this boat? Obviously it will reduce the length to beam ratio, but will I find it makes a massive difference to performance?

    Thanks very much guys.
     
    Last edited: Jun 10, 2009
  2. TollyWally
    Joined: Mar 2005
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    Location: Fox Island

    TollyWally Senior Member

    It won't be as easy in real life as your example in photoshop, which looks very nice I might add. But it can be done and in fact is done all the time with commercial fishing boats.

    With the new motor you will probably have quite decent performance, skinnier boats usually need less power if there is adequate bearing to plane. I'm sure others more knowledgable will chime in with the usual caveats regading strength etc. Good luck with your project.
     
  3. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    You might very well need electric trim tabs with the extra 3' and extra engine weight. Is is a chevy (auto) diesel block V8? If so then no extra weight. I think you will wind up with a great boat. good luck.
     
  4. savagescout
    Joined: Jun 2009
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    Location: australia

    savagescout Junior Member

    Thanks guys,

    Really appreciate the advice thus far.

    I was always planning on throwing some trim tabs on the hull. At this stage I am leaning towards the QL tabs by volvo due to their size on the transom and affordability.

    As for the engine. The original is an old ford v8 windsor mercruiser with alpha drive. The new is a 97 mercruiser 4.2l turbo diesel at 220hp driven by a bravo II leg. The diesel is a VM brand (out of Italy) and apparently is an aluminium block.

    Can anyone recommend the amount of layers of fiberglass I should be using and type of mat to use?

    My idea was to make a mould off the aft section of the hull say 4 feet in length and then glass up an exact copy of the hull in a 3 foot section. My plan was to make the thickness of this section the same as the thickness of the current hull using both Chopped Strand Mat and Woven Rovings.

    Once I pop the extension from the mould I cut the hull and would grind a large taper approximately 8 inches long on both the hull and extension pieces. I would then tab the extension in - using overlapping layers of mat to suit the taper (approximately 5-6 layers would be used here). Then once that has been done. glass over the full extension approximately 7-8 times overlapping each piece by 4 inches.

    I reckon this would be strong enough.

    Any thoughts?
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Taking a mold off the aft sections of the boat will not work. The aft sections taper in plan view and the deadrise likely also changes (yes, even if it's a constant deadrise hull). Meaning you'll have an hourglass sort of thing happening in the areas you extend.

    You can cut the boat at the widest beam, add straight sections, then reattach the stern. This is how commercial vessel are lengthened.

    Will the boat balance, probably not, but you could rough it with tabs maybe. This is much more of an undertaking then you might imagine. Maybe you should rip up the sole in preparation for the changes and see how many stringers and other supporting structures you'll also have to lengthen, to accommodate the proposed change.
     
  6. savagescout
    Joined: Jun 2009
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    Location: australia

    savagescout Junior Member

    I didn't realise that taking a mould would result in that... thanks for the heads up...

    I am most aware of the work involved and am actually looking forward to the large size of the project. I almost prefer the restoration side to actually using the finished product!!

    How are most extensions done?

    Do people take a mould of the centre section and then glass in an extension piece.

    or

    Do people cut the hull at the widest beam, separate the two sections of hull and build an insitu female mould and glass the extension directly to the hull in situ?

    Any recommendation to number of layers/types of mat/ cloth etc???
     
  7. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yes, the boat is cut at the widest beam, which may be at an angle to hit both the rail and the chine's widest portion.

    A mold generally isn't used, as a custom mold for this sort of thing is not especially cost effective.

    Since the bottom and topsides of this hull are basically flat, you just layup flat panels, either in place or on a bench. The laminate would be at least as heavy as the current hull shell. This would be bonded and tabbed to the carefully blocked up fore and aft portions of the hull.

    Of course, getting both fore and aft sections aligned will be troublesome. Fairing in the new sections will also cause some cussing and excessive drinking too.

    In the end, you may have a boat 3' longer or so, but one that has it's centers so out of whack, that she displays all sorts of nasty manners and habits underway. I'd strongly advise reconsidering your idea and looking for an alternative to stretching the hull. This is a difficult thing for an experienced yard to perform well, let alone a novice.
     
  8. Willallison
    Joined: Oct 2001
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    Location: Australia

    Willallison Senior Member

    I know the Savage Scout well. I tried to buy one a couple of times, many years ago, but the owner wouldn't sell. We also used to own a 26' Sonair, which was a custom build based on the Savage Lancer hull. Lovely boat.
    I agree with PAR. Forget trying to stretch the hull - I know someone who did that to a Lancer. The results were ok - but the cost was WAY beyond the replacement value of the boat.
    Personally, I'd flick both the sterndrive options and put an outboard on the back with a pod. You'll gain more cockpit space, get better performance, probably use less fuel... and definitely use less money.
     
  9. Knut Sand
    Joined: Apr 2003
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    Location: Kristiansand, Norway

    Knut Sand Senior Member

    As mentioned by PAR above here; a hull is normally split at the widest area, and lengthened there.
    This hull _seem_ to be parallell in an area behind the cabinroof/ sides and aft, if it is, it can be a little simpler....

    Anyway, don't consider this a small job...

    I like the idea from Willallison, outboard on a pod. new outboard engines are silent, endurable, and not too fuel consuming. Later engine overhaul/ repair/ replacement will be a walk in the park, exept for the money spent....

    And you'll free some of deck space in the cabin, resulting in some of what you wanted. Less work.

    Try to only remove the upper roof, buy some good canvas, try keeping the rest of the windows "as is"...

    PS; don't think you'll need to add a extra wheel on the trailer either....:D :D
     

  10. Willallison
    Joined: Oct 2001
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    Location: Australia

    Willallison Senior Member

    Yes - I agree - on the styling front. This is a 'classic' style of boat. trying to make it look more modern will only end up with a dog's breakfast.
     
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