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Thread: Prop selection.

  1. #1
    Moderator Daveinthebush's Avatar
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    Default Prop selection.

    OK so - 21ft. Seasport 5.0 duoprop. I just got her back from a complete redo. I am getting 35-3600 rpm and 30 m.p.h. Using D3 props and she is topped out. Which is close to before the redo. Will a set of D4's give me more RPM and higher speed? Probably more economical too?
    Volvo doesn't show anywhere that the pitch difference is.

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    Member DRIFTER_016's Avatar
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    If the diameter and pitch are the same between the 3 and 4 bladed props, the 4 will give you better hole shot, better mileage but you'll lose a couple of MPH on the top end. The 4 blade will also hold grip better in tight turns and when the outdrive is tilted up higher to run in shallower water.

    Check out their prop selection charts.
    Lots of good info.

    http://www.volvopenta.com/SiteCollec...er%20Guide.pdf

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    Moderator Daveinthebush's Avatar
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    Not talking about switching between a 3 blade and a 4 blade. The D3's are a duo prop setup. The D4's should be a different pitch for the duo prop.

    Quote Originally Posted by DRIFTER_016 View Post
    If the diameter and pitch are the same between the 3 and 4 bladed props, the 4 will give you better hole shot, better mileage but you'll lose a couple of MPH on the top end. The 4 blade will also hold grip better in tight turns and when the outdrive is tilted up higher to run in shallower water.

    Check out their prop selection charts.
    Lots of good info.

    http://www.volvopenta.com/SiteCollec...er%20Guide.pdf

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    Sponsor potbuilder's Avatar
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    when you go up in size you will lose rpm's, if i remember correctly its aprox 200rpm's with every jump in size. I be more concerned that you are getting the correct WOP throttle rpms with the props you now have. Aren't those gassers supposed to turn up higher than what you are getting ??

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    Member wildwill's Avatar
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    On our 2006 Seasport which had a 5.0 GXI, which rev limits at 5,000 rpm if I recall correctly, we had to step down from the F4's that came on the boat to F3 set. I'd give Seasport or Seward Industrial Marine a call. Really think you should be able to achieve higher rpm's than mid-3's, which expect going up a size may likely prove a step in the wrong direction.

    When we stepped down to the F3 set, my top end dropped slightly, but man did it come alive otherwise. Huge difference in coming onto step and power in the area where we need and use it most.
    Since the World is 2/3 Water and Only 1/3 Land, Figures the Good Lord Intended I Fish More Than I Plow.

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    Ditto what others said above, you need to go down in the duoprop number to increase rpm. I think the rpm change is more like 350 rpm per number change, which is what I saw with my old Osprey when I went down a number. And like wildwill says, it really helped the hole shot.

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    Moderator Daveinthebush's Avatar
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    Getting on step is not an issue. She gets up fine if I take it easy otherwise I blow the water out. At the top she just won't go over 3,500. Today I was getting 3,500 and 31 mph.

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  8. #8

    Default Prop for RPM

    Quote Originally Posted by Daveinthebush View Post
    Getting on step is not an issue. She gets up fine if I take it easy otherwise I blow the water out. At the top she just won't go over 3,500. Today I was getting 3,500 and 31 mph.
    I don't know much about inboards or outdrives, but you need to prop your boat so you are in your maximum RPM range. What I have seen on other 5.0 liters is 4400-4800. Over prop and you will lug the engine which will lead to premature failure. Under prop and you will over rev and blow the engine. Find the manufacturers WOT RPM operating range for your motor and prop your boat to be in that range.

  9. #9

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    You might try this link. http://www.pentamarine.co.th/pdf/propellers.pdf. I think you are heading the wrong direction. I am guessing D1's or D2's but I would call a Volvo specialist or talk with someone familiar with the duo props before dropping money on a new set of props. Something definitely doesn't seem right with your setup now though.

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    Quote Originally Posted by Daveinthebush View Post
    Getting on step is not an issue. She gets up fine if I take it easy otherwise I blow the water out. At the top she just won't go over 3,500. Today I was getting 3,500 and 31 mph.

    your over propped ! what do you mean by blow the water out ?? like others have said you need to know what WOT rpm's should be. Once you know that load the boat with everything you will have onboard when you go fishing, fuel ,water, ice ,beer,food, fat friends etc etc then go see what rpm you get at WOT. If it ain't what the manufacturer sez you need to reprop to get the right rpm's or its going to be a short time till you go to the repower or rebuild shop.

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    A dealer will want to know which model 5.0 you have (GL, Gi, Gxi, etc) and what your drive model and gear ratio is. Then there is a reference chart for WOT RPM and prop selection. You do need more top end RPM, what you are doing now is stressing all the bearings and gears in your drive, at the price of those outdrives, I would get your propping dialed in soon. I have the Volvo Prop charts, so if you can provide the rest of the info above I can make a recommendation. Or provide that info to the dealer you do business with and let him help you out.
    Casey
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    Moderator Daveinthebush's Avatar
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    I talked to a certified Volvo mechanic (the one that did my engine replacement.) on Thursday in Anchorage. We decided to take a different approach. Since the tach is probably original with the boat, I replaced it on Saturday. Will see today if the tach might of been the problem. If not, then a new set of I series D-2 props will have to be next.

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    Quote Originally Posted by Daveinthebush View Post
    I talked to a certified Volvo mechanic (the one that did my engine replacement.) on Thursday in Anchorage. We decided to take a different approach. Since the tach is probably original with the boat, I replaced it on Saturday. Will see today if the tach might of been the problem. If not, then a new set of I series D-2 props will have to be next.
    See if you can borrow a set of props before you buy a new set. Your volvo guy should be willing to do this with you. He should of been concerned what the WOT rpms were when he installed the engine/drive combo( but rather sell,rebuild your motor/drive instead) when it blows up. Its called sea trials so he knows that everything he did is up to specs so volvo will cover any problems with their warranty. He should not have signed off on the install till all systems were up to specs so you the customer was covered.

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  14. #14
    Moderator Daveinthebush's Avatar
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    Quote Originally Posted by potbuilder View Post
    See if you can borrow a set of props before you buy a new set. Your volvo guy should be willing to do this with you. He should of been concerned what the WOT rpms were when he installed the engine/drive combo( but rather sell,rebuild your motor/drive instead) when it blows up. Its called sea trials so he knows that everything he did is up to specs so volvo will cover any problems with their warranty. He should not have signed off on the install till all systems were up to specs so you the customer was covered.
    Doing a sea trial would of been great. But it would mean me, bringing everything to Anch. and re-equipping the boat, hauling it to Wittier, back to Anch. Winterizing it again and the hauling it back to Valdez. He did run the engine but not under a load. Not faulting him, he wanted to do it. I opted out with the logistics concerned. Will see if it was the tach today. He did not have a set of D-2's or I-2's on hand.

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    Moderator Daveinthebush's Avatar
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    Glad I had the mechanic I did. He gave me a used tach and said try replacing the old tach. (Which might be the original to the boat,) And, that was it!! Boat is preforming fine. New tach is registering what it should and problem solved. Simple problem solving sometimes saves money.

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    so what are you getting for WOT rpm's ?

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    Quote Originally Posted by potbuilder View Post
    so what are you getting for WOT rpm's ?
    Yesterday was not a good test day. Too rough. I got up to about 4200 at 32mph before I had to back down. It looks calmer today.

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    Quote Originally Posted by Daveinthebush View Post
    Yesterday was not a good test day. Too rough. I got up to about 4200 at 32mph before I had to back down. It looks calmer today.

    I'd say thats more like it should be. Glad you got it figured out before spending more $$$ for props.

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  19. #19
    Moderator Daveinthebush's Avatar
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    Finally got a good shakedown today. Getting the right rpm's now. 4,000 rpm I am getting 29 mph with a fuel flow of about 10 gph. I am happy with that. She in running like a top and I have to admit that Andy at Noah Marine did an awesome job for me on the repower and preforming an exorcism on the other gremlins' in the boat.

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    Member DRIFTER_016's Avatar
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    Great to hear Dave!!!
    What does she top out at?

    Going to start getting my boat ready this weekend.
    Things are finally starting to open up here in Yellowknife.

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