Drifter skiff

Discussion in 'Boat Design' started by DriesLaas, Dec 30, 2016.

  1. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    Congrats on the build,I have a similar motor ,the transom on my boat is 15" not sure if your motor is a long or short shaft.
     
  2. DriesLaas
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    DriesLaas Weekend Warrior

    That's a good two inches lower than my mounting height.
    I will slot the holes and make the thing adjustable downward by forty mm
    That should do it.
     
  3. DriesLaas
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    DriesLaas Weekend Warrior

    The distance from the throat of the clamp to the ventilation plate is 450mm
     
  4. Angélique
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    Angélique aka Angel (only by name)

    -
    Don't cut the mounting plate off at the top, but drill as much as possible mounting holes at the bottom*, so you can play with the hight till you've found the optimum, at the same time of trying different trim options, after the the optimum is found you cut it off at the bottom side equal to the bottom of the boat.

    * epoxy coat all the holes

    Good luck !

    P.S. - I've responded from the bottom of the previous page (post #45), just saw my suggestion was already above proposed . . :eek:
     
  5. Angélique
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    Angélique aka Angel (only by name)

    -
    BTW, the outboard looks like an 5CMHL, the advised engine transom height for this one is: L = 572 mm (22.5") . . :idea:

    5CMHL: Long Shaft, 2-stroke, 1-cylinder, 103 cm³, Max. Prop Shaft Output: 3.68 kW (5 HP) @ 5000 r/m, Full throttle rpm range: 4500 ~ 5500 r/m, Gear ratio: 2.08 (27/13)
     
  6. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Flat bottom boats will sometimes need the motor mounted slightly lower.

    If there is some deadrise at the transom the water is higher on each side of the prop, plus it flows back together and fills the space quicker.
     
  7. DriesLaas
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    DriesLaas Weekend Warrior

    Angelique, the motor is a short shaft motor, as far as I can tell. Distance from throat of clamp to anti-ventilation plate is 450mm.

    Ondarvr, I have been wondering about the effect of a hull with deadrise, which will clearly allow better "flow" of water to the prop than a skiff type hull. Thanks for that input, it confirms my intuition.

    I will only have an opportunity to test again over the coming weekend, as it was back to work for me today, but there is a way of slotting the holes to have adjustability of height.

    I see the mounting brackets of even large outboards have holes at 3/4 inch pitch, which illuminates my previous question as to sensitivity. I suppose increments in the region of 20mm will be tested , although I am sure the trend will be clear quickly. It is a low powered little motor after all, and I would rather fish than adjust motors at this stage.

    Kingfish season has started here, and I need to put food on the table....
     
  8. Angélique
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    -
    Guess you have the 5CMHS, the advised engine transom height for this one is: S = 445 mm (17.5")

    So if you have the 5CMHS, then you have it 2" lower mounted as the by Yamaha advised height, maybe this works also for Dries' 5CMHL, the advised height - ± 2".

    5CMHS: Short Shaft, 2-stroke, 1-cylinder, 103 cm³, Max. Prop Shaft Output: 3.68 kW (5 HP) @ 5000 r/m, Full throttle rpm range: 4500 ~ 5500 r/m, Gear ratio: 2.08 (27/13)
     
  9. Angélique
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    OK, I've missed your post while I was posting the above.

    Specs say: dry weight 5CMHS = 21.0 kg, 5CMHL = 21 kg / 21.5 kg (S for Short Shaft, L for Long Shaft). But I guess as often in reality it could be a bit more.
     
  10. DriesLaas
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    DriesLaas Weekend Warrior

    For what it is worth (and please pardon the deviation from thread), some confusion is possible with these fish names:

    Kingfish (South Africa) = Blacktip trevally = Caranx heberi

    Couta (SA) = King mackerel OR Kingfish = Scomberomorus cavalla

    Natal Snoek (SA) = Queen/Spotted mackerel/Kanadi seerfish = Scomberomorus plurilineatus

    Shad (SA) = Bluefish = Tailor = Pomatomus saltatrix (though they don't often grow as large as those in the US)

    Kob (SA) = Mulloway = Argyrosomus japonicus

    ALL of which are present in their respective seasons both inshore and offshore, together with various other gamefish and reef dwelling denizens of the deep.
     
  11. ondarvr
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    ondarvr Senior Member

    I fish in many different regions and trying to keep up with the local names given to different species is tough.

    Composites is the same, terms are different depending on where you live, so sometimes communication can be complicated by it.

    As of tomorrow I don't think SA is part of my territory any more, we hired a couple new people, but I hope there's room on the boat for me if I do make it there.
     
  12. DriesLaas
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    DriesLaas Weekend Warrior

    Hi Ondarvr,
    Tell me about it, the interchangeable names in composites have kept me busy as well.
    Believe me, if you ever make it here I can do a hell of a lot better than a tiny little skiff. You can always take it for a spin, and then we can go offshore on a proper boat.....

    How are you involved in composites?

    BTW, I believe I am starting to understand what is going on with the motor height thing:

    In Yamaha's rigging guide, the smaller engines have clamp throat to anti-vent fin distances which are consistently 2.5 inches more than the industry standard of 15" (for short) and 20" (for long). I believe these motors are intended to be used on standard transoms of 15 or 20" high, and are meant to run 2.5" lower.

    As the power of the motors go up, the relevant distances start to converge on the 15 and 20" standard.

    So for me the answer is: cut the motor carrier plate to 15" and forget about it, it will be right. As stated by Tungsten, many thanks.

    This difference between Yamaha shaft lengths and the industry standards has always baffled me in the past....

    This article also enlightened me, and confirms what now seems painfully obvious: http://duckworksmagazine.com/05/columns/max/4/index.htm
     
  13. DriesLaas
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    DriesLaas Weekend Warrior

    Ventilation was caused by motor depth, it is now sorted
    Speed went up to 11.5 kits, which is what I think is going to be the best for this motor / boat combination.
    Boat much drier than I expected, and slamming is not a problem.
    In flat water the boat turns well, but it loses direction when running in a chop, almost as if it stalls out, and I think this can be dangerous in some conditions. I will add some bits to improve directional stability.
     
  14. DriesLaas
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    DriesLaas Weekend Warrior

    Small update:
    Went out yesterday, to start working out how to rig the boat for fishing (a nice part of the job!)
    The water was not bad, as smooth as can reasonably be expected.
    The boat works, I can stand and cast, and for bottom fishing sit down and fish comfortably.
    The interesting thing is the "hybrid" behaviour when turning at speed. If you shift bodyweight into the turn so that the hull is heeled, while turning, the boat turns a LOT better. You have to get your head around it that you can affect the behaviour by turning the boat like a surfboard, hence "hybrid" character.

    Still have to put the first fish onboard though...
     

  15. DriesLaas
    Joined: Aug 2009
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    DriesLaas Weekend Warrior

    So a few months have passed, and I have added a few more hours at sea with the Drifter. Also had opportunities to re-think some design aspects, and learn about the practicality of ideas.
    The boat works as well as I hoped. The total weight is a lot more than I thought, 85 kg for the hull, so I have to use a trailer to transport and launch. The center console works, I am now building a simpler deck lay-out with a box seat. This opens up the deck considerably.
    One of the main problems with this type of configuration is a lack of steering arc because of the long tiller arm extension. In normal use it is OK, I have felt the need for turning sharper on occasion.
    I have built a norwegian tiller type extension, with a push-pull extension, and attached a staff to the gear selector. I also heath-robinsoned a throttle control onto the end of the extension. This limits the required amount of movement while operating the boat, which is a BIG advantage in rough water. The tiller is also now out of the way, over the side deck, and this creates even more available space to work on. The deck is finished, and the hull will be sprayed after completion of the running strake experiments. So far so good, let's see where this goes.
     
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