23’ Inboard Prop Size

[fishinfootballer]

Repowering our 1976 Inboard with a 315hp vortec motor in the next couple of weeks. Tranny is Borg Warner 1.52:1.

What prop size should we use with this set up? Looking for fastest cruise possible.

[kevmen]

Full disclosure - I am no expert on props, but for what it’s worth I just repowered my 78’ inboard with a crusader - 330 HP same transmission as yours. When the mechanic took it for a sea trial he was doing 35 knots at 5000 rpm’s, 26-27 knots at 3500 rpm’s. I have a 16x16 Nibral prop.

This was on an empty boat with 30 gallons of fuel and 2 guys on it. WOT is 5200 rpm’s for my engine, but I am happy with the cruise - 5 knots faster than my old engine, but that’s with an empty boat. I may need to go to a 16x15 prop, not sure yet. As I said I am no expert, but reading all the posts on this site about it - seems you have to do some trial and error, but maybe the 16x16 or 16x15 gives you a starting point. I am sure you will get a lot of feedback. Lots of very knowledgeable people on this site. Good luck with the repower!

[fishinfootballer]

Kevmen, I appreciate the response! I’m currently running a 16x16 prop. But it’s a right hand rotation motor and prop. Current cruise with 260hp Merc is 22. With wide open throttle around 33

[kevmen]

I think we own the same boat! My old motor was a 230 HP - cruise at 22 WOT was 30 - the new engine made a big difference even with the same prop. Seems like you are on the right track - a little trial and error and you should have it nailed down to what you want.

[Outrageous]

I tried a 16 x 16 and went back to a 16 x 15. I do a lot of drifting and rip running and found that it works better for the eastern end of LI which is where most of my fishing is done. I also like that it helps when loaded up and sea conditions are less than ideal. The cruise was a bit better w/the 16 x16.
I turn LH w 315 hp or so. Vortec BW 1.52 - 1 Best advise I can offer is to try either and see what works best for how you run and what you do. Keep us posted!

[kevmen]

Ran the boat - finally - only got to 4600 RPM with the 16x16 and a full load - ( 90 gallons gas, 4 people, all gear on boat) thinking I am going to have to try the 16x15 - it ran fine at cruise to me, but I think the extra 100 HP deceived me - a lot more power than I had before. Engine specs call for min 4800 - 5200 WOT with 5000 being optimal. I am afraid not changing the prop will put extra stress on the engine at cruise. Any other thoughts?

[Old'sCool]

I agree....

[John3325]

I just repowered my 23 IB with a 330 hp crusader, pretty much identical to Kevin's.

We put a 15 X 14 prop on it and it spins 5200 at WOT. Sea trialed with 3/4 tanks full, life jackets, safety gear. Problem is, I went to the bank today and with 4 guys fully loaded to fish (35 gallon live well in stern, rods, tackle, coolers, ice, etc.), I was doing 16 knots at 4000 RPMs with the tabs buried.

Calling the shop tomorrow, but I think I need a 16 X 16 LH or 16 X 15.

Need more prop to grab and push, right now with a load the boat struggles to get on a plane. I'll gladly sacrifice rpms to have good hole shot and good cruise while running offshore.

UPDATE 25JUL19: Pulled the boat and it had a sheet of barnacles on it. The bottom paint definitely had issues and loaded the boat down with growth. Took it out yesterday and I was back at 4000 RPMs doing 23 knots. WOT I am doing about 29-30 knots. 2 nm per gallon at 4000 rpms. Prop is a 15 x 14, has a very minor cup on it.

I called Accutech and their recommendation was to add a more aggressive cup to the prop for some more bite since I can afford to drop a few hundred RPMs. They insisted that I keep the prop I have since I hit my redline on the dot at 5200 RPM. With that said, I have a few fishing trips planned this weekend and we'll see how the boat goes loaded before I send a prop out for tuning and cupping. Keep you all posted.