Prop change: any thoughts

[Rainmaker]

I need to pick up a spare prop for my eTEC 225HP. I figure at the same time I should try to get it right at this point. I have been running the boat for a few year and the one I have is close but not quick enough to get on plane. Curently it takes me close to 9 seconds to get up on a slide. I need to cut that back a bit if possible.

I took the boat out and charted a few RPM points today:
@ WOT I run 5600-5700 RPM 22.5GPH and 41mph on the GPS
@ 400RPM 10.2GPH 24.5mph
@ 3000RPM 7.5 GPH 9.8MPH but not on a plane

I am currently running a 3 blade SS Viper prop (I had a little bit of cup added though) the prop is 14.75/17P

I am considering going with a 4 blade in the same size but I am not sure if that will solve my planing issue or if I should go down in pitch if I go to the 4 blade. I am thinking the added cup and the 4th blade may be a wash.

Any advice on what to change to? What will that do to my top end?

Any of the prop gurus on the board have some suggestions?

[Blue_Heron]

Hey Rainmaker,
Your top end number looks to be in the right ballpark. And your WOT RPMs are not low, something you would expect to see if the engine was over propped and lugging to get on plane. The fact that you're not on plane at 3000rpm, and your engine is on a bracket, may point to a balance issue rather than a prop issue. I suspect you may be tail heavy.
Dave

[Rainmaker]

I never thought of the weight issues, but I am not inclined to think I am tail heavy. I put a large armstrong flotation bracket on it. The boat acutally sits a little Bow down in the water at rest. I carry (and had in the boat when I test ran) about 70#s of lead in the bow in the form of deep drop tackle. The amount of lead changes week to week but I normally have some extra weight up there.

By the way, my numbers were taken with 100g of fuel in the tank (holds 150).

Any thoughts on the 4 blade prop? Anyone running a 4 blade? Could it help?

[76Red18]

Viper creates too much bow lift and makes the stern dig at lower speed especially in a cc. If you have the money to spend on a 4 blade cyclone or rev 4 it should help. An older style OMC SST works well also. Not the SST II though, too much bow lift also.

[Bushwacker]

Rainmaker, I know our boats are much different, but when I repowered from my old 300 lb V-4 on the transom to a ~430 lb motor set 30” back on a bracket, I had a similar problem. With the old motor I could easily plane at 12-13 mph, but with the new motor and a 3B prop, it was terrible . .min planning speed was about 20 mph, an obvious sign of a very stern heavy boat! It would either just plow along as you describe at 2500 rpm/6-7 mph or with a VERY slight nudge to the throttle (less than 1/8”), it would want to run 3500-4000 rpm and 30+ mph! Part of this is due to the near-vertical torque curve of the E-Tec starting at 2000 rpm, where it makes the transition from very lean stratified-charge mode to a much richer mixture. However I noticed it was a little less sensitive with a 19” prop than a 17”, so I concluded that maybe I needed a little more blade area to absorb all that power. I tried a 4-blade prop, and eureka, problem solved!

I now run a 4B SS 15 x15 PowerTech and I can plane at about 2500 rpm/12-13 mph and boat has an awesome hole shot – literally jumps on plane in 3-4 sec at about 45% throttle. Max rpm is about 5450 with max load. The non-linear throttle response is now easily controlled. (BRP changed a $15 throttle cam on the 2009 150’s that reduced this throttle sensitivity a bit.) I never use full throttle to get on plane, as it tends to throw folks out of the boat!

Your max rpm indicates you’re not overpropped. Although CC’s tend to be more stern-heavy than a Seafari, your last post sounds like you may not be stern heavy either. If you’re too bow heavy, I can see how that could be almost as bad as being too stern heavy. Balance/CG location can make a huge difference in how a boat performs and rides, and that’s why Carl Moesly (a former pilot) used ballast tanks on his race boats to adjust trim/CG for optimum performance in various sea conditions. He also put the gas tank right on the CG on the original production SeaCrafts, so trim wouldn’t change as you burn off fuel! Have you tried moving gear around to see if that makes any difference? Also, what is your min-planning speed?

I have a couple of 4B props you’re welcome to try; a 14x18P Aluminum 4B Michigan Vortex is my spare, which turns about 5550-5600 at max load; also have a 14.125 x 20P SS 4B Michigan Apollo that is too much pitch for my 150, (max rpm about 5250 light load/ 4600 max load) although maybe your 225 could spin it faster. I don’t know if the prop shaft/spline configuration is the same on our motors, but the Michigan 2-piece hub system also used by PowerTech will allow the props to be used on any motor with the right spline adapter piece. Just send me a PM if you want to try any of my props.

You must be digging quite a hole in the water and dragging a hell of a wake @ 9.8 mph if you’re not on plane! I normally run either on plane or at hull speed (fully settled in water) at 900 rpm/5 mph and 10 mpg. Most folks don’t realize how fast gas mileage drops when you run faster than hull speed when in displacement hull mode. The I-Command gage that calculates instantaneous mpg says that at 1100 rpm/5.5 mph I’m getting about 7 mpg, so it doesn’t make much sense to burn 30% more fuel to run 10% faster!
Denny

[Fr. Frank]

Denny, you're exactly right. Sounds like a prop geometry problem, with possibly added CG issues.
First step, go to a 4 blade, but drop the pitch by at least an inch.

Propeller geometry can make a difference of more than 30% in your thrust efficiency. When I ran a V6 Merc on my Seafari, I switched from a 3 blade Mirage 19"P to a 4 blade PowerTech 16.5"P.
I went from:
5900 max rpm at 43-44 mph (30% slip) and 4000 rpm at 32 mph (26% slip), to
6100 max rpm at 52-53 mph (8% slip) and 4000 rpm at 34 mph (10% slip).

I don't know what the fuel economy was with the Mirage, but with the Powertech, I cruised at about 3100-3200 rpms and 24-25 mph from Key West to Marathon and got very close to 3 mpg with the V6 xR4.

Today, with my 90 hp Optimax, I can cruise at 4100 rpms at 24-25 mph and get 5.1 mpg.

[Rainmaker]

Thanks for the input. And yes, I normally do not run at 10MPH since I dig one heck of a lot of water. I am not sure on my min plane speed, I assume it is upwards of 18 mph though. That is just something I have not given much thought to.

It sounds like I am thinking in the proper direction. 4 blades sounds like the direction to go. I am thinking I start with 4B 14.75/16P and work from there.

Now for another question: Is there a prop shop in the Stuart/PSL area that lets you play with the options before or after you buy? I hate paying to determine what I need and then paying again to get it.

Thanks for the offer on your spare props, I hope I can find a local prop shop that can help but I will let you know if I need to take you up on it. I am going to buy a prop regardless since I do not have a spare currently. I just want to get the proper one so I can put my viper 3B away as the spare.

[Bushwacker]

A spare is an absolute must for Bahama trips! If you think prop prices are high here, you don't even want to know what they'd cost if you had to buy one over there! It's also a good idea to carry a spare plastic insert if you run a prop with the newer 2-piece hub system.

Bobby Soles is a good shop in WPB area; don't know if they have a shop up your way. You might give them a call and see if they work with any dealers up that way. ARG in Riviera Beach has some used props they'll let you try. If you know anyone at the BRP test center in Stuart, I'm sure they could get you dialed in real quick! A friend of mine used to be their Chief Engineer, but I believe he has retired.

A low min planning speed is generally indicative of a well balanced boat, so it's worth paying attention to. It's especially nice to have in a 20 when it really gets snotty, but probably less critical in a 23 with more weight and deadrise. Denny
Denny

[Rainmaker]

A spare is an absolute must for Bahama trips! If you think prop prices are high here, you don't even want to know what they'd cost if you had to buy one over there!

I agree, I spun a hub over in the Bahamas a couple of years ago. I asked a local that I have known for years for a ride to Marsh Harbor to get it rehubbed. He laughed, but then reached under his Bar and handed me a brand new SS prop and said "this should fit". It did. When I asked how much he wanted for it, he laughed again and said "you can't keep it" so I used it for the rest of the trip and to get home. I brought it back a year later. That could have been a real issue for me, but every so often I have a lucky day.

I may reach out to Bobby Soles prop shop because I know they will let you return and resize if you buy a prop from them. It is a bit of a drive, but if it saves me from making a bad purchase it will be worth the gas.

[Bushwacker]

I always had Bobby Soles torque test my hubs before a Bahama trip. At least with the new 2 piece hubs, you can carry a spare hub. When I was making those trips in late 70's, prop prices in the Bahama's were about 3X the price in the states!

You might start with an aluminum version of the prop you want if he has one. The Michigan Vortex and Apollo are same basic prop; the Vortex is the aluminum version and the other is SS. Aluminum is easy to repitch, and that way he can dial it in before you spend big bucks for the SS version. He says he can't do anything with the SS prop except reduce diameter or grind some cup out of it.