prop question 24 pathfinder 250 SHO

[Texas Craig]

I'm brand new to the forum and also the proud new owner of a Pathfinder 24. The boat has a Yamaha 250 SHO four stroke on it and maxed out at 5200 RPM on the test ride. anyone here running a similar rig that could give me some info on the prop they are running. I don't particularly like the trial and error method of Prop selection. I'm leaning toward a four blade. any help would be greatly appreciated.

[Nag Juice]

I had the same combo before and spun a Power Tech OFX3 21" and that seemed todo well. A 19" 3 blade has way too much slip. Call Marcus at PT to dial you in

[FROZEN]

TC,

Calling PT is a good start. I owned a prop shop in Florida for 20 years and the following are the caveats I would give to owners on a daily basis for them to prop a new boat.

1. The only thing that matters to preserve the integrity of your motor is the prop performance at WOT. With the boat loaded as you normally use it, WOT has to be between 5000 to 6000 RPM for the big bore 250 SHO. The peak of the HP curve for this motor is 5500 RPM, and is theoretically the only engine speed where it delivers 250 HP. More or less WOT RPM means you are pushing the boat with less that 250 HP. With the boat new and clean, the best performance and top speed has to meet these parameters. Once there, If you want better speeds, you need a bigger motor or a lighter boat.

2.Boat weight is the single one item in this process that makes owners unhappy. Many owners of new boats spend a lot of money to tweak the prop and get it perfect for them. THEN load the boat with all the things they need to make boating fun. Cast nets and tackle, full coolers with beverages, safety gear, full livewells, additional electronics, fuel full, and of course, 6 of the allotted 7 wives, girlfriends, and buddies. It's amazing how quickly the boat weight increases. This simply increases drag in the water requiring more HP, or less top end / cruise speeds. Keep the prop as delivered for now, load up the boat as you will use it, THEN tweak the prop to suit your needs. Always test the boat loaded with about 1/2 fuel and 1/2 of the live wells /wash tank full of water. You would not believe the number of customers who are unhappy with the performance of their newly tweaked prop a short time after loading the boat.

3.Now do your speed tests. In calm water, with the boat loaded as you will use it, trimmed for max RPM at WOT, write down the speed and RPM at WOT. Modern boats can be scarey fast, so be careful and safe. I rarely use my boat anywhere close to WOT, but that is how you prop a boat to assure proper engine loading across the HP curve.

4. Take those numbers to a reputable prop shop or PT, and, with a few questions, they can nail it the first time. If after the first adjustment, you are still wanting better hole shot, they can fix that too. But only after you have a prop that nails the peak of the HP curve. For you, 5500 RPM. Remember, the rule of thumb, 1" pitch = about 200 RPM. 1" more gives 200 less, and vice versa. Cupping is about 75 to 100' and improves hole shot.

5. Modern props are progressively pitched, meaning different pitch measurements at different places on the same blade. Always use a reputable, large prop shop or the OEM to tweak your prop. They should have either OEM pitch blocks or computer measuring equipment to do a pitch change, and the OEM pitch specs. ALWAYS ASK for these items before you let someone pitch change or repair a prop. These items are very expensive for a shop and not all shops possess. If they don't have, find another shop that does.  In the old days, you could pitch change any prop 2" in either direction. There are some props now where pitch change is not possible because of the complex geometry of the prop. Yes, you're in to replacing, or swapping out the entire prop. 

if you need to talk to me further about your project, please PM me with a phone number. Congrats on the new PF, you're a lucky guy,

[JEM]

It looks like you nailed Prop 101!!!   Great primer on props that we all need to be reminded of occasionally.   This post needs to go up to the permanent prop thread.

Thanks!

[CG RYAN]

Definitely needs a sticky for that post, nicely put. As far as props, where in TX are you located? I currently run a OFX4 20" and always have a couple other props laying around. Let me know if you would like to try mine. I am in the Houston area. 

[Bruce J]

I have the same boat and motor with the factory hardtop. After trying the factory/dealer supplied Yamaha 21", I couldn't get sufficient RPMs. I swapped out to a PowerTech OFX 4 18" and like it pretty well. Top speed is about the same at roughly 51-52, but it will run in the mid to upper 5500-5800rpm range.