Propping a 58 Viking

That’s gonna be a considerable stack of dough just to see what might happen. What about adding some cup to your existing wheels at the next haul out. You can get feedback from the prop shop once they’ve got ‘em.

Diameter makes a world of differences that most folks can not apprehend.
A quality (real world) can reason it out but why try to re-invent a wheel, the factory has already done so much for you.
You think these guys just guess and install a set of wheels for you to live with?
I'm sure hundreds of hours were spent to get a good, starting sized wheel installed to deliver.

What is the factory spec?? Call them up and ask about improving, per your use what way you can go.
BUT, The factory spec is always where to start from.

Almost anytime I’ve seen diameter added to props the result is overloaded motors. Of course as Ralph points out it depends on where you start from.

Are those 2300rpm motors? You say you’re almost at 2400 so that’s less than 100rpm to burn. If that’s the case there’s no way I would increase prop diameter. But based on your last post you look like you’ve already made up your mind. Good luck.

I'm into diameter and blade area. I have lots of past personal projects where I have proved this to myself.
A little more blade surface = more traction.
You just want to eat up 100 rpm, ad pitch.

Do you have a set of spare wheels? Do you need a set?

Your operating well now and in no hurry.
Just keep a new set of wheels on your x-mas list and ask around the real prop shops. They may share some thoughts and a loaner prop set to experiment with.

Let's say you do, and you get those 2 knots max back. That's what, 1 knot at cruising speed? Probably less.
I wouldn't lose any sleep over that, let alone money.
And that's without considering if you must shorten the pitch to avoid overload, 'cause in that case you can forget getting back the 2 lost knots.
In fact, you said that you're almost making 2400, and 2350 is what you should really aim at, not 2300.
So, the room you can actually play with is how much, 30 rpm?
Be happy with what you've got, I say.
Most 24 years old engines around would tell you they are envious of yours, if they could talk!

Don’t know if this comparison will help but with a 1995 54 Viking MY with 820 Mans with a dinghy, etc on the bow I burn 60 gallons an hour with genny at 2050 RPMs. This is at 21 knots or so. I had what I believe to be original wheels on it and replaced those with 5 bladed Veems from Black Dog in MD and I now turn 2400 on my best day (winter (cool temps) and fresh bottom). In the summer with shark skin on the wheels and higher temps I will lose 50 RPMs. I wouldn’t touch your props. You will lose your cushion. I am sure others will disagree but slightly underpropped I will run at the upper end of the cruise RPM knowing my engines are not stressed. I have been told more than once that properly propped MANs like being run at the upper end of the cruise RPM. If you want to help your performance my best money was spent blueprinting the turbos. You could feel the difference and see the difference (much reduced smoke). Of course that is assuming yours need it which based on my experience they probably do.

No I don’t mind sharing at all. I will have to go home and look up the invoice. I don’t believe the invoice listed the blue printer but I am pretty sure he was in and around Palm Beach. Yes I am happy with the work. I will try to look it up tonight and get back with you.

You could always contact Veem, fill out their boat info/specs form and then see what prop diameter and pitch they recommend. You may find they don't recommend much different then what you already have. But as others have suggested, sounds like you're in a pretty good range already. Likely lots of other areas to spend those boat bucks

Back in 2014 the cost per turbo was $2,515.00. No freight or labor to remove and replace. I am not sure who did it. It is not listed on my invoice but I believe it to be DMS in West Palm Beach. I did not see a 2 knot difference about a knot faster, with much better hole shot, higher boost and lower pyro temps.

Your welcome. Keep us posted