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whale tail/hydrofoils, worth it?

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  • whale tail/hydrofoils, worth it?

    Any of you guys notice a difference with your SIB using a hydrofoil? Handle better, plane better, steer better? I have a 12 ft. Saturn boat and use a 9.9 Johnson 2 stroke short shaft. Wondering whether I want to buy one. Why don't manufacturers just incorporate these into the motor?
    Saturn SD 365
    1980 Johnson 9.9 2 stroke

  • #2
    Re: whale tail/hydrofoils, worth it?

    Originally posted by gotmehooked View Post
    Any of you guys notice a difference with your SIB using a hydrofoil? Handle better, plane better, steer better? I have a 12 ft. Saturn boat and use a 9.9 Johnson 2 stroke short shaft. Wondering whether I want to buy one. Why don't manufacturers just incorporate these into the motor?
    I have never used one. However, I would say that the boat manufacturer's design their boats so that these should not be required. If you are having issues that suggest you need a "whale tail" then one or more of the following are probably an issue:

    - motor not mounted correctly
    - motor is the wrong size for the boat (either too big or too small)
    - boat loading is incorrect/unbalanced

    I would check that all of these are correct before looking to a "whale tail".

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    • #3
      Re: whale tail/hydrofoils, worth it?

      We have run 9.9 and 15 HP Johnsons and Evinrudes on our boats and there was no need for those devices. They do add lower unit drag while allowing lower planing speed to correct boat and load problems though.

      The manufacturers know what they are doing and spend engineering time to design lower units. For every one who needs help with planing, the majority have no problem with the factory lower units.

      A hydrofoil could very well help you, but the only way to find out is to attach one to your lower unit.

      Ssobol did a good job listing possible problems. I will add that you may need a 9 or 8 inch prop to allow the motor to rev up.

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      • #4
        Re: whale tail/hydrofoils, worth it?

        Originally posted by fbpooler View Post
        We have run 9.9 and 15 HP Johnsons and Evinrudes on our boats and there was no need for those devices. They do add lower unit drag while allowing lower planing speed to correct boat and load problems though.

        The manufacturers know what they are doing and spend engineering time to design lower units. For every one who needs help with planing, the majority have no problem with the factory lower units.

        A hydrofoil could very well help you, but the only way to find out is to attach one to your lower unit.

        Ssobol did a good job listing possible problems. I will add that you may need a 9 or 8 inch prop to allow the motor to rev up.
        I have a 9 1/2 x 10 inch prop, the motor is a 1980. I think I do a good job with weight distribution keep most weight toward the front of the boat in a trunk that fits between the tubes. The only thing in the back is me on an empty cooler and the 3 gallon gas tank which I never fill completely.
        Saturn SD 365
        1980 Johnson 9.9 2 stroke

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        • #5
          Re: whale tail/hydrofoils, worth it?

          Evidently you have no need for a hydrofoil. I had to go to a 9 in pitch stainless with a 15 HP on a 14 ft fiberglass as the motor did not perform with the 10 inch. The rigid fiberglass hull is much easier on the motor than an inflatable. The 9.9 handled the load pretty well with an 8 in pitch prop but of course much slower.

          The 9.9 on a 10 ft Avon planed the boat but was sluggish. There is a good chance that your motor with the 10 in pitch prop is not developing full RPM or power. Have you a tach available?

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          • #6
            Re: whale tail/hydrofoils, worth it?

            Play around with motor trim. I went in one hole (no comments) and the boat responded in a major way. It literally stands on end to get on a plane... but it porpoises like the dickens, next time out I change the trim one hole back in the other direction. a slightly slower holes start is ok by me... you have to experiment to see what is best for your combo... and THEN start changing out parts from there.j
            Saturn 365/ Johnson 15 hp

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            • #7
              Re: whale tail/hydrofoils, worth it?

              I may try one on my 1976 Chrysler 15hp/ Achilles 12'2" combo. It runs fine and gets on plane very easily with just me but I would like to see how fair back I could cut the throttle and remain on plane with a hydrofoil. 40 bux is not to much of an investment to me to see.

              https://www.facebook.com/photo.php?v...type=2&theater

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              • #8
                Re: whale tail/hydrofoils, worth it?

                Here is a post of note for you on another site:

                Will a new prop help - RIBnet Forums

                The gentleman had roughly the same problem you describe and was very satisfied when he put the 9 in SST prop on the motor. It blows my mind that a 10 in prop would be considered standard for a 9.9 unless it was on a 12 ft jon boat.

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                • #9
                  Re: whale tail/hydrofoils, worth it?

                  Originally posted by fbpooler View Post
                  Evidently you have no need for a hydrofoil. I had to go to a 9 in pitch stainless with a 15 HP on a 14 ft fiberglass as the motor did not perform with the 10 inch. The rigid fiberglass hull is much easier on the motor than an inflatable. The 9.9 handled the load pretty well with an 8 in pitch prop but of course much slower.

                  The 9.9 on a 10 ft Avon planed the boat but was sluggish. There is a good chance that your motor with the 10 in pitch prop is not developing full RPM or power. Have you a tach available?
                  I don't have a tach but could probably get my hands on one. With just me the boat moves well, but last time I was out with my friend who is probably 230 lbs in the front and me 150lbs in the back, the boat was sluggish. Which, is probably just from the added extra weight. I did try playing around trim position that day and it didn't help much.
                  Saturn SD 365
                  1980 Johnson 9.9 2 stroke

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                  • #10
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                    Re: whale tail/hydrofoils, worth it?

                    I just ordered the doel fin from Amazon and will test it this weekend to let you know my impressions/results

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