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3 Blade prop to 4 blade prop

Discussion in 'Post Yacht' started by Rich M., Feb 6, 2021.

  1. olderboater

    olderboater Senior Member

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    So, let me be sure I have this right. You have a boat you like but it's overpropped. You just paid $3.5 million. You'd recommend selling it for $2.7 million and buying another boat you don't like rather than repitching the props. :eek: Yes, I know you were joking.

    Unfortunately, I've been around so many cases of wrong props on new delivered boats. On small boats on the lake it was a regular issue with US builders and it appeared to be worst, or at the very least most noticed, in higher performance boats. However, recently, I've seen the problem from several well regarded builders in the US, Europe and Asia. In some cases, I think they're testing with virtually no load on the boat. Other cases, I have no idea what their problem is.

    Now, I will add one issue on new boats and that is that many I've had have gained performance, gained RPM, during their break in and up to their first 50 hours. However, if RPM is on spec at the outset, I'm happy with gaining 50 or so.
  2. mapism

    mapism Senior Member

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    Indeed.
    It's rather obvious that if I already owned an incorrectly propped boat I wouldn't sell her at a huge loss just for that reason alone.

    BUT, if I were considering a brand new 60-70' boat (none of which the last time I checked are sold for peanuts...), my short list would rather include builders who did their homework, rather than trust buyers to beta test their products.
  3. olderboater

    olderboater Senior Member

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    I'm afraid in that size range and that price range, you'd likely have to choose the lesser of evils as none are buttoned up as tight as they should be. These are production models and the quality assurance isn't what it should be. However, when we look for brands to buy, they're not as bad as others. Sad we have to look at it that way.
  4. mapism

    mapism Senior Member

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    Not knowing to which brands CJ was referring to, I must take your word for it.
    But I'm aware of some boats/builders in that size bracket whose production consistency, also through pretty long production runs (6 to 8 years), has always been maintained. And prop sizing/optimization is obviously a relevant part of that.
    But if you would argue that among boatbuilders these are more the exceptions rather than the rule, I'd never dare saying that you're wrong! :)
  5. Capt J

    Capt J Senior Member

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    Both are long term, well known builders. I've seen it on several new yachts from Europe.....air temp/water temp are much colder than South Florida. They zealously propped it where it barely made RPM's there, then 30F hotter air temp and 20F hotter water temp and motors make less HP. I've seen it on half a dozen new builders over the years.
  6. DOCKMASTER

    DOCKMASTER Senior Member

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    In most cases I think you will find the prop shops are simply passing hull and engine info to the prop manufacturers who make the recommendations. Pretty much all the prop companies have their own form you fill out and then they make their recommendation. I was pleasantly surprised when I bought my new Veem Interceptor props how well they nailed the right prop on the first try. I didn’t even have to adjust the strips. I was also surprised how wide their allowable weight ranges were before it changed the pitch. The hull type, waterline length, ratio and other factors effect more than weight.
    NYCAP123 likes this.
  7. NYCAP123

    NYCAP123 Senior Member

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    I've spent my life trying to learn as much as I can, but choosing a prop still confounds me. As you point out though there is so much more involved besides 'a 4 blade prop will give more at the top end and a 3 blade prop more in the mid-range'. For some things there are just so many factors to consider that you're just better off putting yourself in the hands of the professionals.
  8. DOCKMASTER

    DOCKMASTER Senior Member

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    If you decide to get new props I have been very happy with my new Veem Interceptor props and recommend them. You get some minor adjustability with the strips and arguably some of the best props made today. I went from 4 blade to 5 and changed diameter and pitch a lot due to a repower and gear ratio change. Despite all the changes, Veem selected a prop that works perfect.
    Please let us know what you decide and how it turns out.
  9. Stainless45

    Stainless45 Member

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    I'm interested to hear how you make out, I'm on Long Island too. My 1990 46 has 692's and 3-blade props with "26" and "25" both stamped into each hub. I only got 20 knots out of her this past summer after purchase, and I'd like more. It's been recommended that I have Johnson Machine in Freeport take a look at my wheels. I have no idea if they are original or not.
  10. Rich M.

    Rich M. Member

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    I will. I was hoping somebody on this website had some Relevant information right now I'm waiting for Chris to send me up his knockoff hub from Florida I'll take the props off and bring them over to Larry Junior see what he has to say. If you keep your boat at the Whaleneck ask some of the old timers who Chris is. I worked for Chris for 12 years. Just out of curiosity what kind of RPM are you pulling out of it
  11. Stainless45

    Stainless45 Member

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    I had to leave Whaleneck because of the southerly weather exposure, my starboard rubrail got destroyed back in November, and I'll be looking for a new home. The engines spun right up to 2300 with no problem, I suspect I'm under propped.
  12. Rich M.

    Rich M. Member

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    Sorry to hear about the boat damage 20 knots sounds a little low in the speed end of things I kept my boat at Wantagh park for a couple of years 14 with my Egg Harbor and two with the Post it is very protected but it only has 30 amp service some spots have two plugs though and only a couple of spots will fit the Post you should take a ride over there and see if they have anything left even after the lottery I know there was open spaces there last year
  13. RT46

    RT46 Senior Member

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    not sure, I think your cruise with the 92s should be closer to 24-25 knots
  14. RT46

    RT46 Senior Member

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    i damaged my rub rail in that storm also.
    One section is like $300 and another $200 for shipping, it comes in 20' lengths.
    I got the exact stainless insert at Freeport Marine.
    i have not ordered the rub rail yet.
  15. Stainless45

    Stainless45 Member

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    I ordered the Rubrail with a minimum purchase of 20 ft but had it cut into 7' lengths for shipping. I may have some extra left over I can give you. And yes I am hoping for 24-25 knots, my props are at Johnson Machine in Freeport now, going to add a little more pitch
  16. OutPost

    OutPost Member

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    Nice to see some local south shore Posts on here! Bit of a thread derailment but you can find me at Tobay more often than not. PM me if you'd like to share contact info offline.
  17. DOCKMASTER

    DOCKMASTER Senior Member

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    Curious - how much pitch are you adding? What was your WOT before?
  18. Stainless45

    Stainless45 Member

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    He deciphered the stamps and said they were originally 26"x26". somebody removed an inch of pitch, probably when the previous engines were worn out. These 6-92's have only about 500 hrs on them. They ran right up to 2300-2350 rpm without delay. Top speed I ever saw was 20k. Going back to 26x26
  19. DOCKMASTER

    DOCKMASTER Senior Member

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    Sounds like you were propped about right at 25”. Sure hope you don’t end up overloaded with the added pitch. Those 692’s won’t like that.
  20. Stainless45

    Stainless45 Member

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    1100 HP should be able to get me 24-25 knots without a struggle. We shall see