Am I over-propped? - First update!

[Capt Bill]

All the discussion about props, RPM and top end that have been going on here got me to thinking about my boat. Smooth, clean, painted bottom, curtains up, outriggers off, 175 gal fuel, 10 gal water, some fishing gear and 2 people, I am turning 15 1/2 x19 SS props, 5100 rpm at WOT, topping out at 40-41 mph.

Yamaha's specs on these 2002 F225's, are from 5000 to 6000 rpm WOT. That's what my owner's manual states, and that's a pretty big spread. Since I am no where near fully loaded, I think I might be over-propped. Should I drop to 15 1/2 x 17, or ???

Would like to hear from some of you on this.

edit: I might add that when I bought the boat last year from the original owner, she had a waxed bottom; no paint, and turned up several hundred rpm higher.

 

[ocnslr]

Bill, see if you can borrow (test) a pair of Yamaha SWS 15.25" x 17".

Assuming that your 5100 RPM is trimmed out, then you should be several hundred RPM higher. Lightly loaded you should be darn close to the 6000 mark, so you are still in the upper half of that 5k-6k range when loaded more heavily.

However, the Yamaha web site gives the 15.25" x 19" as the props used for this test in 2001. http://www.yamaha-motor.com/assets/...etin_otb_4StrokePerf_HPV6_225hp_053-GRW-A.pdf

Not sure what it may be, but something isn't right....

 

[Capt Bill]

Brian, they may in fact be 15 1/4. With the boat in the slip, I did my best to accurately measure center of prop shaft to tip of blade, but I easily cold have been off an eigth of an inch, times 2.

I like your idea of borrowing (even renting) a set of props, but I have no idea where. Local dealers are probably out of the question, but I will check.

I would like to be mid-5k loaded to go.

 

[NOTHING ELSE MATTERS]

On my Bimini 306 with f250's i had 15 1/4x19 SSII. I think you should go below that. Maybe 15 1/2x17 ? That would give you aprox. 300 more RPMS.

 

[gradyfish22]

To properly prop a boat you need to have the boat full of fuel and gear, you want the boat to be around 5800-6000rpm for those engines to be spinning the right props under that condition. Even if you spin 6000 with a light load, you will fall flat on your face and have no power when you are fully loaded. I know guys who pick props to run under their normal operating condition which may not be fully loaded, but then they run the boat on one of those few occasions with full fuel and heavier gear and encounter some sporty seas and wonder why the boat handles like crap and could not stay on plane or have the power to get over waves when needed. I would say you are with-out a doubt running the wrong props. You are likely burning more fuel then you need to and losing speed at your cruise as well. A new prop that is the right size/pitch will be to your benefit, as well as the engines which right now are likely working harder then they need to or were designed to. I believe many guys have been running merc props lately, partly because merc had a program over the summer where you could put a down payment on a prop purchase, and would get loaner props to test until you found the correct one, and then you paid in full for your purchase. The down payment was to ensure you bought their props as well as a security deposit incase you did not return them or you mangled them by hitting something. That may be something to look at, I've heard many guys getting better numbers on their Yammies running merc props. I considered doing this but had too many other things to purchase this season and my props turn up to 5800 with full fuel and 6000 with a regular inshore load.

 

[ocnslr]

I think that's what I said...

Lightly loaded you should be darn close to the 6000 mark, so you are still in the upper half of that 5k-6k range when loaded more heavily.

When "C-Time" had a single 250HP OX66, I worked with Bay Propellor in Chesapeake, VA and tried at least five props before deciding on a PowerTech OFS4-17". I got got 5450 RPM lightly loaded, and 5250 heavily loaded. The four-blade was a huge improvement with a single engine on our boat.

When we were looking for better props for the F150s, I tried about four sets. Decided on PowerTech OFS3-16". Those props in 17" were just a bit too much, so I dropped an inch. Now I can hit the rev limiters when trimmed out, so I am going to have Bay Prop add a bit of cup - enough to drop 100-150RPM.

The props we replaced were the Yamaha "Black SS", 13.75"x17". They were not bad overall, but not enough bite in the chop. Bay Prop ran them through a polishing machine for me, and they look like any polished SS props now.

Propping correctly is an inexact science, but there is a technique to doing it.

Bill and Reidun were with us in Solomons, and he knows how "C-Time" performs with her current PowerTech props.

Concur with the comment that many Yamaha owners are finding good numbers with Merc props. But across the range of performance, the Yamaha SWS and SWSII props are hard to beat. They have a new four-blade prop now as well, for the big engines - the HS4.

Brian

 

[Seafarer228G]

Capt. Bill,
I've heard Short's Marine in Millsboro will allow you to return props if you don't like them.

 

[Harleyfxdl]

I had a 15 1/2x19 Yamaha SS on my boat when I first got it. I was yurning 4800 rpm with normal load. I switched to the same prop in 17" pitch and now I'm turning 5100-5200 same conditions. I think the throttle plates might not be fully open. I should be running 5800-6000, getting about 38 mph.

 

[gw204]

It's been my experience that propping for a light load will only result in a 200 or 300 RPM decrease when fully loaded...and performance changes are minimal.

Do you remember how much fuel was in the boat when you got it? Seems to me that the addition of bottom paint, and having the tank 3/4+ full wouldn't drop your RPM 400 of 500 (if that's what you mean by several hundred). So, I think something else is amiss. Have you done other things like putting in new spark plugs, new fuel filters, etc.?

Mrs. GW204 and I are heading to OC in 2 weeks. If you want, I can bring both sets of props that I have (14 x 19 Yamaha wheels and 15-1/4 x 19 Merc Mirage Plus) for you to try.

 

[Capt Bill]

So many good replies to my question. Good stuff, here on GG, so thanks. I did go over to Shorts Marine today, but the guy I need to talk with won't be in until tomorrow, so I'll check on their prop loaner offers, if any. And Brian, I might take you up on your generous offer to bring those props to OC. Will let you know well before.

When I bought the boat, she had nearly full tanks, but I know that fuel was not ethanol-laced, like what is in there now. She was also empty of any gear, and had a waxed-gelcoat bottom. I have a notebook somewhere with the performance specs from the sea trials, and if I remember, they turned just about 5500. Now, with some gear, bottom paint, and ethanol fuel, I am only turning up 5100. Oh, and yes, Brian, I have changed the plugs since then (NKG LFR5A-11). I know the bilge is dry, so I'm not hauling around half a ton of water. I can't think of anything else that is different.

I was on Power Tech's website, and they say their 4 blade prop is well suited for ocean-going boats. Wonder if I should consider a 4 blade?

I'll see what happens tomorrow when I call Greg at Shorts.

 

[hotajax]

New Prop?

I WAS turning 4900 at WOT, prop was a Yamaha 15 1/2 X 19. I dropped down in diameter and got a Stiletto 14 1/4 X 17, and now I turn 5600 rpm with about 3/4 of a tank of fuel, full gear, and just myself aboard. From talking to different people, there's simply no formula for getting it right. It's trial-and-error until you get the rpm's you need.

 

[Capt Bill]

Called Short's today, and spoke with Greg. They have a few "loaner" props, but not L,R pairs. They don't load out new props, so it's pretty much whatever they can scrounge up from the used stuff on hand.

I also called Power Tech today, and they advised that it is best to keep the larger diameter, and drop the pitch, so they are recommending as first choice, a 4 blade 15 1/4 x 16, or as an alternative, a 3-blade 15 1/4 x 17.

Anyone here ever switch from a 3 to a 4 blade? Did they live up to your expectations?

I wish I could try those 4 bladed props before I buy them.

 

[gw204]

Capt Bill,

Try to find a Merc dealer that participates in their prop-demo program. I looked but there's something wrong with the site right now. If memory serves, you front the $$$ for a pair of wheels and then get to try as many sets as you like until you get the performance you're looking for. I also seem to remember something about the demo props being painted a bright blue to make them easily identifiable (those aren't the ones you keep).

Also, try going through Merc's Prop Selector. That will give you a good starting point. I bet you end up with Mirage Plus or Enertia.

http://appcenter.mercurymarine.com/propSelector/home.do

Good luck!

 

[B-Faithful]

Call Prop Gods in FLA. Yes you will pay a little more in props but Ken will give you knowledge to what works best. You can also swap out props that didnt work for the cost of freight. Considering the cost of buying and selling new SS props, it will save you in the long run.

If you do know what you want. Shorts has the best prices. I bought my Enertia for my last boat from them.

Good luck!

 

[Capt Bill]

Since my original post, it's been raining hard here, and too windy to do any further testing, until today.

I took her out to the bay for some WOT speed/rpm tests. Temp was about 78 deg, winds calm to 5 mph, seas calm, boat lightly loaded with fuel about half capacity, one person. I ran 3 round trip courses across the bay, a distance each way of about a mile and a half.

WOT turned up 5400 max and 42.5 mph, in one direction, and almost the same; 5300 and 42 mph the other, on each run. Since the tach only reads 2 most sig digits, I believe the 5300 was close to 54, as it occasionally jumped to 54, then back. Post engine seemed to consistently hit 5400, while stbd engine bounced between 53 & 54.

I noticed that the boat seems to have a slight tendency to turn to port; took ever so slight amount of wheel to starboard, to run straight. When I got back, I checked the trim tabs. Port tab is dead center; starbpard engine tab is turned slightly to stbd, pushing the boat toward port. I will center both tabs next haulout.

I am overpropped, but it is not as bad as I first thought. I'm still thinking about those 4 blade props; maybe 15 1/2 x 17. Does anyone here know if it makes a significant difference between using a larger diameter, lower pitch prop like the PowerTech size mentioned above, and the Merc 4 blade Revolution 4, which is a 14 or 14 5/8 x 17 or 19? Seems to me the larger prop would provide better bite, and better low speed handling.

on edit: "overpropped" is what I meant to type

 

[ocnslr]

Glad to hear you could get out, Bill, and thanks for the update.

You are, indeed, "overpropped" (not underpropped), and need to get those WOT RPMs up a good bit on those F225s.

You could probably be comfortable with a simple move to Yamaha SWS props, 15.25"x17". The drop in pitch should give you 300-400 more RPM, and the same top speed.

Can't comment on the comparison between PT OFS4 and Merc Rev 4.

Good luck with the process.

Brian
P.S. Did you talk to Max or Jerry?

 

[CKJR]

I had 19"s and turned 54-5500, Dropped to saltwater series 17m 17" props and turn about 5900 to 6000. Was not happy with the mid range bite especially in a sloppy ocean, I tried a pair of the merc 4 blade 17" turning wot 5900 to 6000 and i find overall bite and performance good. If you should need any other specifics, please drop me a pm. Charles.