3 Blade prop to 4 blade prop

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. 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.

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.

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.

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!

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.

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.

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.

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.

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

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.

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.

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

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.