RiverRat My shiny new 1971 Dyne

Discussion in 'Hydrodyne 18' started by RiverRat, May 2, 2007.

  1. RiverRat

    RiverRat Hydrodyne 18 Specialist

    Joined:
    Sep 30, 2006
    Messages:
    508
    Location:
    Shoreview, MN
    Boat Model and Year:
    1971 Baby Dyne
    Ski Team:
    Twin Cities River Rats
    Re: My shiny new 1971 Dyne

    That goes along with what Must-ski motors has been saying about the Rebels. I am still trying to figure out why our dealer sold a Viper to our President as a replacement for an SST. Especially since I had him picking up a Rebel for me at the same time.

    On a slightly different note, I got the wedge installed a week and a half ago. I only got to use it twice since then, but it seems to have helped with slow speed planing and keeping the bow down on larger pulls. I also started with the motor mounted on the second hole up, and moved it up to the full up position (2 holes higher than before) and picked up about 200 RPM at WOT. I didn't take a close look at it on plane before chaning the height, but now it looks like the water hits the plate about 6 inches back (at around 20 mph), and begins curling around. I am guessing this helps with slow speed planing, as there is more surface area hitting the water, and it's at a decent angle of attack, when trimmed all the way down with a wedge.
     
  2. jim

    jim Hydrodyne 18 Specialist

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    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    Re: My shiny new 1971 Dyne

    Raising the motor will help unless it causes the prop to ventilate in the turns. Most prop shops and boat dealers have no idea what a good ski prop is in my experience. You are on the right track for an 18.

    Here is what I did. I bought a new aluminum OMC 17 and tried it. The pitch was too high for swivel. I took it to a shop and asked to have the cup removed and got a very strange look from the prop guy. He said he did not think he could do it, but his dad probably could. The cup was removed no problem. I got the RPM and push that I wanted and noticed that I seemed to be getting stern lift. What I really had was less stern dig. My motor turns 6100 at 47.

    I did the same with my daughter's 17.6 and got too much RPM so I had them repitch it to an 18 and got the RPM and push that I wanted. This was at a different and better prop shop. He had no problem with any mod that I wanted to try.

    Here is what I would do if I were you. Buy a BRP 17 aluminum prop from a good prop shop. Run it and see what you think. Take it back and have the cup removed and re-evaluate. A 17 Aluminum prop can be pitched from 15 to 19. Some where in that range should satisfy you I would think. I don't think it will be a good long term prop on that big motor, but it should give you an idea of where to go with the more expensive steel props.

    jim
     
  3. jim

    jim Hydrodyne 18 Specialist

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    77 Dyne 18 I/O converted to Outboard
    Re: My shiny new 1971 Dyne

    By the way, after you arrive at the height that you like, you can probably have the midsection shortened by the amount the motor is raised. Then put the motor all the way down, but the lower unit is at the height you want.That would get the cowl down a little and help with the pitch up by using a slightly lower pull point.

    Now we are talking motor mods. I love custom stuff.

    jim
     
  4. RiverRat

    RiverRat Hydrodyne 18 Specialist

    Joined:
    Sep 30, 2006
    Messages:
    508
    Location:
    Shoreview, MN
    Boat Model and Year:
    1971 Baby Dyne
    Ski Team:
    Twin Cities River Rats
    Re: My shiny new 1971 Dyne

    I'm not real sure how long the motor will be on the boat, so I don't know if I really want to go shortening my short shaft just yet. Now, if I had a brand new 300 E-tec, and it was going to be for personal use only (not getting worn out by constant ski team use) it would probably hang around for quite a while, and I might consider that.

    I think I am going to go to the prop shop that I mentioned earlier around here and see what they can do for me. Thanks for all the custom input Jim, I will take that with me and see if they can help me out. They did tell me that if I bought a stainless prop from them, they would exchange or rework it until I was happy.
     
  5. jim

    jim Hydrodyne 18 Specialist

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    77 Dyne 18 I/O converted to Outboard
    Re: My shiny new 1971 Dyne

    I just want to caution you about one thing. Most prop guys will tell you that the cup adds about 1 inch to the effective pitch. My experience is that it has way more effect than that, and I was playing with aluminum props that have less cup than steel props as a rule. If you buy a steel 17 and take out the cup it may rev way too much and you can only change a steel prop 1 inch in pitch I am told. It is a risk. I think the Rebel does not have much cup, so you might be ok.

    That is why I made the suggestion that I did.

    jim
     
  6. jim

    jim Hydrodyne 18 Specialist

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    77 Dyne 18 I/O converted to Outboard
    Re: My shiny new 1971 Dyne

    If you are going to start with a steel prop, here is how I think I would do it.

    Step 1--Rebel 17--evaluate

    Step 2--if rpm is too low, remove tip cup only--evaluate
    if rpm is ok, try an 18 or 19--evaluate--remove tip cup and evaluate

    Step 3--if rpm is still too low, remove all cup--evaluate.

    Step 4--if rpm is too high add pitch

    Step 5--if rpm still too high add cup to the inner portion of the trailing edge as required.

    Step 6--tell all of us how to do it so we don't have to spend all of that $$$$$$$$$$

    jim
     
  7. Must-Ski Motors

    Must-Ski Motors Hydrodyne 20 Specialist

    Joined:
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    Location:
    Beaver Dam
    Boat Model and Year:
    87 20 single; 93 MC Barefoot 200; Nautique 196
    Ski Team:
    Beaverland Must-Skis
    Re: My shiny new 1971 Dyne

    River Rat -
    The VIper is the newer style swept blade polished prop. The older props which I prefer have a rounded trailing edge where the Viper has a straighter and more cupped trailing edge. It is not as ideal as the regular old SST. They have apparently discontinued the old 16 pitch that I really like. The new 16 Viper no doubt has the swept blades and the straight trailing edge. It is also a higher rake prop than the old SST's. This is why I do my prop shopping on Ebay, because you can see them and determine whether it is the old style.

    I hope to be able to do a comparison test soon. Our triple rig now has 4 blade 15 pitch Cyclones by BRP and those seem very nice. The effective pitch seems close to 17, but they are a bit smaller diameter and do not have much cup. I want to try one on my 225.
    I would recommend watching Ebay for a 15, 16 or 17 with the old rounded ears. For ultimate speed holding the 15 or 16 will be the ticket.

    I have the following props to test right now:
    15 sst
    16 sst
    17 sst
    17 Viper
    15 cyclone 4 blade
    15 Rebel
    17 Rebel
    19 Rebel
    15 Mirage (Merc with flo torq hub)
    17 Mirage

    I hope to test them all on the 225 HO on one day
     
  8. jim

    jim Hydrodyne 18 Specialist

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    Location:
    FL
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    77 Dyne 18 I/O converted to Outboard
    Re: My shiny new 1971 Dyne

    How about an up close picture of the tip cup in a Bebel. Hmm, that sounds southern. :D ;)

    jim
     
  9. RiverRat

    RiverRat Hydrodyne 18 Specialist

    Joined:
    Sep 30, 2006
    Messages:
    508
    Location:
    Shoreview, MN
    Boat Model and Year:
    1971 Baby Dyne
    Ski Team:
    Twin Cities River Rats
    Re: My shiny new 1971 Dyne

    I will see what I can do about getting some pictures and see if you see things the same way I see them.

    When you say the blade is cupped, is it over the majority of the blade surface, or mainly just near the trailing edge?

    With what I have seen on most of the stainless props, they tend to have quite a hook right at the trailing edge. I would think that would cause quite a bit of turbulence. Not sure how that would affect the propulsion (you would think a rocket scientist would be able to figure that out though), but it can't help keeping the table smooth.

    Now I'm starting to wish I had followed my degree more closely so I would have access to wind tunnels or water tunnels and all that fancy test equipment.
     
  10. jim

    jim Hydrodyne 18 Specialist

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    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard

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