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Propeller Recommendations

Discussion in 'Technical Discussion' started by DOCKMASTER, Sep 10, 2019.

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  1. Capt J

    Capt J Senior Member

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    I see Veems on a lot of the newer boats I run and you can tell the difference. Vibration on all of them with the Veems is pretty much non existant. Even in reverse and when maneuvering. They perform well also. I've seen old sets of interceptors and the plastic strips are still in them, might be worn a little bit, but not a big deal IMO.
  2. DOCKMASTER

    DOCKMASTER Member

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    Boat was hauled yesterday and went into the building this morning. The current blade tip clearance with the existing 28" diameter props is 5.5". Less than we had hoped. So if I were to go up to a 33" prop this would leave us with 3" clearance which calculates to 9%. Based on this the new prop recommendation from Veem is now to use a 32" prop which leaves 3.5" clearance or 10.9%. They said 15% is desired but 10% is the bottom of acceptable so the 32" is what they recommend. We can go down to a 31" or even 30" but they said the blade overlap makes future repair (if necessary) very difficult. No final decision made yet.

    Also found out the boat is heavier than I thought. She weighed right at 72,500 and that's with empty water tanks and about 250 gals of fuel capacity remaining. So that puts her right about 76,000 with full water and fuel in the existing configuration. I know we will shed at least 2,000 lbs for the repower, probably closer to 2,500 but I'll use 74,000 to be on the safe side. However, it looks like this is unlikely to change the prop recommendation as it is likely still within the range quoted but I'm verifying.
  3. Donzi 54

    Donzi 54 Member

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    That's interesting, I have not ever measured but by this photo of mine looks more then 3.5" and that's with a 33/43 wheel. Also note the updated rudders that we installed.
    upload_2019-9-27_13-52-19.png
  4. DOCKMASTER

    DOCKMASTER Member

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    Very hard to tell from this photo. From the angle it looks like the blade may not be at its closest point to the hull? But what the heck, it is obviously been working well for you regardless.
  5. PacBlue

    PacBlue Senior Member

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    10% tip clearance is an acceptable minimum for a conventional setup, I have seen less only on boats with propeller tunnels. There is some sound deadening material that you can put inside the hull over the prop area if you have access in case you want to address any potential noise or feedback issues.

    I suspect the struts are different on both of your boats (Donzi 54 and Dockmaster). They could have a different vertical drop. Now that the boat is level, what shaft angle can you measure? What is the the length of your strut barrel, you typically want at least 4 times the shaft diameter? And what is the OD of the aft end of the strut barrel, you want the OD of the forward end of the propeller barrel to be equal to or less than the strut barrel OD?
  6. PacBlue

    PacBlue Senior Member

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    How was she weighed? Load cells or other?
  7. Capt J

    Capt J Senior Member

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    If you're going to bigger shafts and changing the struts you could go to longer struts to give you more blade tip clearance.
  8. DOCKMASTER

    DOCKMASTER Member

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    The crane has built in load cells. We pre-weighed all the rigging and the cradle.
  9. DOCKMASTER

    DOCKMASTER Member

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    It’s not reasonably possible to go with longer struts. Doing so changes the shaft angle and throws everything off. The shaft logs are matched to the existing angle. I’m not going to mess with those. I’ll just go with the 32” prop likely. I will be going up to 2.75” shafts but we will utilize existing struts and shaft logs and line bore for bigger shafts.

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