19 foot CC and Transom Bracket

Discussion in 'Powerboats' started by johnnythefish, May 24, 2017.

  1. johnnythefish
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    johnnythefish Junior Member

    Would it be possible to add an Armstrong type floatation transom bracket to this hull - and would it drastically affect trim with a 150 HP 4 stroke engine.

    Would it be possible and advisable to add a transom bracket on the following hull? It would be fitted with a 150HP engine and am worried about drastic change of trim angle; but have also read some very positive reviews on transom brackets.

    Classic 19 (C19) - Study Plans http://bateau.com/studyplans/C19_study.php?prod=C19
     
  2. TANSL
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    TANSL Senior Member

    That boat has been designed without transom brackets and that should be for some reason. It seems clear that, as he thought his designer, the boat does not need them. Therefore, it is very important to know what effect you want to achieve with the transom brackets to be able to say if they are suitable or not, if they are going to get the results you are looking for or if you are going to introduce some changes to the boat or its equipment that justifies the use of brackets.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    150hp is overkill with that hull, in my opinion, even a 90 would give good performance. The boat has little deadrise to speak of. The reason for wanting to install a bracket is what, an increase in internal space ? Any gain in speed is more of academic interest in a boat that will be cruising at 20 knots in average conditions, there is the potential to be absolutely hammered in that boat if it leaves the water in a choppy sea. If you need more room, get a longer boat, a 150 four-stroke could easily power a 23 footer with a shallow-vee bottom. Why involve yourself with complexities of changing plans to change to a pod, it does set up additional stresses on the hull. as well as changing the dynamics underway, though I'd say with an 8 foot beam, the boat is probably as likely as any to be adapted to a pod, but 150hp is too much power anyway, unless you envisage heavy loads.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Give him a call and ask yourself. Jacques Mertens is approachable and will provide the answers you need, plus max power recommendations to boot.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    150 hp is specified as the max, but seriously a 1200 pound hull with 12* deadrise will go into orbit if the throttle is opened out on the open sea, with 150 horses.
     
  6. johnnythefish
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    johnnythefish Junior Member

    Ok guys thanks for all your answers ... to clarify, I already have built this boat already and reasons to consider a transom bracket are to gain 2 feet of cockpit space.

    Reasons for putting a 150 on, is that I have just got an amazing deal on one and I would like to replace the existing engine. Before someone suggests trading the new engine in, that is not a realistic soln where I live. So ... I have a new 150 4 stroke Yamaha and I am going to make use of it.

    The transom is 20 inch and the new engine shaft is 25 inches. Because I am going to have to do some work on the boat anyways, I started to think about other sons - and a floatation bracket is one.

    Jacques - "doesn't like brackets on boats less than 20 feet"... because of a risk of porpoising; but he says the transom is strong enough if I insist!

    Having a big engine doesn't mean I have to drive the boat at full throttle - indeed both the engines best RPM and the most comfortable speed will be about spot on at 20 kts with 3500 RPM.

    I am not against the idea of a bolt on "hull extension" that goes all the way flush with the existing hull if this is what is needed to produce the floatation needed to hold that engine up.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    The weight of that engine, more than HP, worries me, I think you are going to need an extension that is no longer than necessary, wider than usual, and in line with the existing bottom, height wise. Otherwise it will be asking too much, on what is basically not a hefty boat. But you have 8 feet of beam, which, unless there is a lot of outward flare to the topsides, means you have enough waterline beam for it to be feasible.
     
  8. johnnythefish
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    johnnythefish Junior Member

    Thanks Mr Efficiency - do you know if this sort of "bolt on" extension has been done before and if so, how the results have turned out? I suppose if the extension basically becomes a continuation of the hull, then it would have a similar effect to stretching the hull in length by say 2 feet?

    This is different of course to an Armstrong bracket, where you are raising the motor and setting it back for reasons of speed as well as extra space?
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    There are many boats around with pods that are extensions of the existing botton, albeit not usually full width, so it is not the same as stretching the boat by that length, which may well be undesirable anyway for boat handling. Certainly a raised pod/engine set-up will act differently, and with a heavy engine you have, not likely to be successful in my opinion. If you fit a pod that is level with the bottom, and still find you have excessive squat, there is the ability to fit trim tabs. You should also choose a generous rake angle to the pod engine mounting face, to get adequate in-trim if needed. Of course level mounted pods offer little or nothing in the way of better performance, you have increased the wetted area, the only incentive is the gain in internal space.
     
    Last edited: May 26, 2017
  10. johnnythefish
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    johnnythefish Junior Member

    Mr Efficiency - once again many thanks for your input. I took the time to take some measurements of the hull today and have posted a picture of it on blocks.
    Some pretty basic maths gives me about 200 liters of buoyancy if the edge of the "hull extension" came inline with the edges of the motor well cutout - 55 inches wide.

    Could someone explain the advantage of having a step? And also if one didn't have a step to the bracket whether there would be some advantage in tapering the transom bracket up/ and or inwards.

    My main interest is not in high end performance, but more space, and perhaps better efficiency at trolling (below planning) speeds.

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  11. Mr Efficiency
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    Mr Efficiency Senior Member

    It is 72" across the chine at the transom ? I might have expected a bit more for an 8' overall beam. You cannot expect any improvement in trolling speed efficiency. The theoretical high speed performance gain from raised pods is due to the prop working in water which is less affected by the frictional drag of the hull ahead of it. You are right to not bother trying to gain anything there, it would be miniscule. 55" wide sounds reasonable to me, certainly I would not chance a narrow pod for fear of unbalancing the boat, you have a balancing act where a full width hull extension might be too much, and a slim pod too little. You might err slightly on the side of narrow, because it would be relatively easy to pad it out on both sides rather than cut it back, if found to be forcing the bows down, or stiffening the pitching motions making the boat wet or otherwise unruly.
     
  12. jorgepease
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    jorgepease Senior Member

    What is the difference in weight between this motor and the lighter one. Probably not more than a hundred pounds but your shifting weight back some so need to compensate and shift some other weight forward or put a flotation bracket to compensate. Pods wont cause porpoising if they are set right, jackplates will. Pods act like wheelie bars so normally the bottom is angled up to allow the boat to tilt to proper planing angle. I don't see any problem with doing it, draw it out on paper, it's not too hard to achieve that balance.
     
  13. leaky
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    leaky Senior Member

    Wish I had a better picture handy, can't find them at the moment, but here is one I took back in March or so showing my 16 ft starcraft with a 5 inch jackplate/setback-bracket, plus 2 inches of spacer between the bracket and the hull, plus some wedges between engine & bracket, with a 110 HP Johnson (yes I stickered it as an 85 HP to match the boat's max rating). It's a fairly shallow V that if I remember right is something like 65 inches wide at the transom.

    The reason I did it was I just thought it was a cool thing to do, allowed me to bring the transom height up, get rid of the engine well, and since I run in shallow water the jackplate has some advantages in helping you get out of jam without putting the engine at a funny angle.

    Porpoising is not an issue but getting it to jump up on a plane in a reasonable manner was - the transom just didn't have much angle in it and trimming full down wasn't enough, the prop was basically at an angle parallel with the bottom of the hull at full down, maybe even trimmed up a little, versus creating any force pushing the bow down; given the extra weight this was not enough to jump the boat up on a plane so I added 2 sets of wedges, maybe only needed 1, but it worked and I've been running it that way ever since.

    I bet you can put a bracket on that hull, it will obviously give you deck space. You very well may need to tinker around with things to get it to run right. Some things will be better, some worse I'm sure. Another option to consider is if you went up 5 inches in shaft length on the outboard you could build the transom up 5 inches and then should be comfortable enough to loose the engine well all together with the extra freeboard. You'd still have some engine rigging hanging into the deck but it would be much more open then previously with very little change in how the boat will run - technically your center of gravity would go up a little but I doubt it'd be noticeable.

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  14. leaky
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    leaky Senior Member

    Something else to mention - I'm a big fan of putting the max or near max HP on most outboard boats in this size range. When you get into boats with twins, like a 24 footer that is rated at 450 HP that's different.

    What you run into is on smaller boats the weight you add has much more impact on how they perform, it's not about top speed, it's about the boat performing the same way regardless of whether you are alone or are with your 3 buddies, and not beating the hell out of the engine in the process.

    The particular boat in the picture, with the 50 HP I had on it for years, would do 30 with just me and got up on a plane nicely.. 2 people was a max of about 25 on it's best day and had a little trouble planing.. 3 people was a max of about 20 but might not come up on a plane unless somebody ran up to the bow, might only do 15 against the tide running the engine wide open.

    Now with the 110 the boat only really does about 45 MPH tops but it will still do > 40 MPH with 3 of us on board and jumps up on a plane extremely quickly no matter how you are loaded. Normally I zip around at about 3000 RPM and that's somewhere around 30 MPH - engine is barely working where the old engine was always running at or nearly full throttle.

    Jon
     
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