Deck Boat Prop Recommendation - HighFivew?

[LipschitzWrath]

Took my new deck boat out this weekend for the first time. 2015 Tahoe 215 XI with 260hp 5.0 Mercury. Was VERY disappointed with the performance all around. With just my GF and I on the boat, probably took us 15-20 seconds to get up on plane. With 7 of us on the boat, probably somewhere between 30-60 seconds. On top of that, top end speed sucks, only getting about 40-42 MPH at 3900 RPM. Also worthy to mention this boat will spend the majority of its time on Flaming Gorge reservoir in southwest WY, elevation 6500'. Here are the details, according to the sticky:

1) Issue - Very slow to get on plane. Top speed also nowhere near advertised and RPM's seem very low for WOT.
2) Current prop - Mercury Black Max aluminum 3 blade, aluminum.
3) Current dia/pitch - 14.5 x 19
4) WOT RPM/Speed - 40-42 MPH @ 3900 RPM (4 people on boat)
5) Engine - 2015 Mercury 5.0 EFI 260hp; Drive - 2015 Mercury Alpha One 1.47 ratio
6) Boat - 2015 Tahoe 2015 XI, 21'6" long, I estimate the weight somewhere in the 2200-2300 lb range

I am not a top speed fanatic and don't mind giving up some top end. I want an awesome hole shot as this boat will spend a lot of its time pulling a wake/knee boarder or tube.

What is making this worse is that before we bought the boat, we read a boattest.com review and they said the boat got up on plane in 3.2 seconds and had a top speed around 51 MPH. I know the altitude has a negative effect, but we are NOWHERE NEAR those figures.

I called the boat dealer and he agrees the prop is wrong (then why did he put it on?), and is leaning towards something in the 16-17 range. I have been reading and am kinda leaning towards the HighFive propeller, but read somewhere that the 17 pitch model H5 is different construction and should be avoided?

Who can shed some light?

 

[steelespike]

If I remember right each 1000 ft elevation costs ab out 2% So your down about 12% some of that is eased with the fuel injection.
Based on my estimate you could be down about 31 hp.Don't assume everything is right cause its new.Check that the throttle opens all the way.
Might just have a plug wire off or 2 transposed.

 

[LipschitzWrath]

If I remember right each 1000 ft elevation costs ab out 2% So your down about 12% some of that is eased with the fuel injection.
Based on my estimate you could be down about 31 hp.Don't assume everything is right cause its new.Check that the throttle opens all the way.
Might just have a plug wire off or 2 transposed.

I can certainly check those things tonight. I guess I would have expected to hear misfires if plug wires were off / wrong.

I will check. I guess that would be a relatively simple fix, but it seems like a dog.

 

[LipschitzWrath]

Okay, checked the plug wires and throttle. The plug wires are definitely okay. The throttle seems to be opening all the way - maybe a 1/16" shy of the open throttle stop.

I spoke to my dealer today about a prop exchange. He definitely agrees that a prop change is warranted. Now for the bad news. He says that "his calculator" (turns out to be Mercury's website calculator) is recommending an 11 pitch!!!! I told him I think that is way too aggressive of a prop change but he is pretty adamant. He says that the calculator is usually close to right on and that he's seen "some pretty radical prop changes recommended." The example he chose to use was changing from a 23 to a 17. I said that makes more sense because those are normal prop sizes. I've never heard of ANYONE running an 11 inch prop on a boat with 260hp. I said maybe he should send me two prop sizes because I am pretty sure I am going to over rev the motor at 30mph with an 11 pitch.

He promised to call Mercury this morning and speak with a live human being. I jumped on and used the calculator and came up with recommendations of 14-16 pitch.

Can anyone bring some sanity to this discussion?

 

[Maclin]

My gut feel is with your 14-16 pitch. That elevation makes a lot of difference even with fuel injection. Fuel injection has better driveability over a non-adjusted carb but there is still limited air to bring in to add fuel to and power is down.

If you think you might ever run it at lower altitudes then I would try to keep the 19p.

This may take two steps to get it dialed in spot on. For now I would try to get a new 17p in the budget and try it from somewhere that does prop exchanges. Or maybe a 4 blade 16..... The 17p will be a good way to get meaningful numbers to zero in even closer to what your boat wants "up there".

Most times I have been over-propped and then went to a proper prop pitch the top speed actually went up 1-2 mph as the slip% came back in line and the engine was allowed to rev freely. I have never lost mph due to correcting an over-prop.

I do think the 11p was out of bounds

 

[SkiDad]

seems like you may have motor issues - i would think you should still plane in 10 seconds at that altitude - that boat is more like 3500 lbs

but for reference my neighbor had a 21' searay with same engine and about same weight and ran a 21 pitch and it planed in 7-8 seconds and ran about 45-50 You could try a 17 pitch high-five but seems like that is masking another issue.

you could try putting a timing light on each plug to see if you are getting spark.

 

[LipschitzWrath]

Thanks for all the replies.

I'm still waiting to hear from the dealer but I did call Midwest Propeller in Kansas and they agree that 11P is WAAAYYY too little prop.

You are correct, the boat dry weight is 3500 lbs. Fully loaded, we are probably looking at more like 4200 - 4500. Sorry about that.

I agree about finding a place that will do prop exchanges and I am sure I will. The customer service with this guy has been poor to say the least.

As far as the motor issues, I guess I can rule it out. I'm kind of a motor head (not on boats) and I'm pretty sure I would be able to tell if something with the ignition system wasn't working correctly. I have a timing light but no motor muffs.

 

[LipschitzWrath]

My gut feel is with your 14-16 pitch. That elevation makes a lot of difference even with fuel injection. Fuel injection has better driveability over a non-adjusted carb but there is still limited air to bring in to add fuel to and power is down.

If you think you might ever run it at lower altitudes then I would try to keep the 19p.

This may take two steps to get it dialed in spot on. For now I would try to get a new 17p in the budget and try it from somewhere that does prop exchanges. Or maybe a 4 blade 16..... The 17p will be a good way to get meaningful numbers to zero in even closer to what your boat wants "up there".

Most times I have been over-propped and then went to a proper prop pitch the top speed actually went up 1-2 mph as the slip% came back in line and the engine was allowed to rev freely. I have never lost mph due to correcting an over-prop.

I do think the 11p was out of bounds

So you agree with 14P-16P?

But you are recommending I try a 17P?

Isn't the rule of thumb 200rpm per inch of pitch? So dropping from a 19P to a 17P would get me up around 4300-4400, which is at the lower end of the RPM range for that motor. Which brings up another thing...

I read that Mercury recommends 4400-4800 RPM for all their V8 outboards, yet the boattest.com review said they attained 51.8 MPH @ 5200 RPM. How is that possible? Wouldn't there be a rev limiter?

 

[Maclin]

Regarding this..."but I did call Midwest Propeller in Kansas..."

Great bunch there. During one of my "boating" stints I was fortunate to live about 5 miles from them. Knew of them before that, they were/are THE Go-To guys in that region. Had a couple of sets done, always enjoyed dropping off and picking up with them

 

[LipschitzWrath]

Regarding this..."but I did call Midwest Propeller in Kansas..."

Great bunch there. During one of my "boating" stints I was fortunate to live about 5 miles from them. Knew of them before that, they were/are THE Go-To guys in that region. Had a couple of sets done, always enjoyed dropping off and picking up with them

Agreed. Got that tip from a guy I work with that has been an avid fisherman for years. Says he refuses to do business with anyone else. I confirmed with them that they will exchange props with me through the mail (so long as I don't damage them).

 

[Maclin]

On the 14-16 I was adjusting for what there would be actually available. I do think you will need to try a couple of options, and I would start with a 17. Of course taint my money !

You may need to look up your specific engine model. I know on 350 Mags their RPM upper end recommended was higher. It may be the same for a multi-port 5.0 but I only play a boat expert on the internet :lol:

 

[LipschitzWrath]

On the 14-16 I was adjusting for what there would be actually available. I do think you will need to try a couple of options, and I would start with a 17. Of course taint my money !

You may need to look up your specific engine model. I know on 350 Mags their RPM upper end recommended was higher. It may be the same for a multi-port 5.0 but I only play a boat expert on the internet :lol:

I am calling Tahoe/Mercury right now to confirm max RPM. EDIT: Just got off the phone with Tahoe. They said 4900-5200. Now I called Mercury and they said 4600-5000. So I am definitely low.

I am not worried about the money. I want my brand new $40K deck boat to get out of the water in a time that can't be measured with a sundial. I am mostly concerned with hole shot, as top end runs will be rare for me. I know that fuel economy sucks up there anyways.

So based on that, would I be better served with a 4/5 blade?

 

[LipschitzWrath]

Spoke to both Tahoe and Mercury for recommended max RPM.

Tahoe = 4900-5200
Mercury = 4600-5000

 

[Maclin]

Conventional wisdom goes with a 4 blade for good grab with a heavier style boat. Continuing that thought stream, 1 pitch down from what a 3 blade was getting to by way of RPM. The top speed will be down a bit but way less slip so good grab in the water. Sometimes too much grab if the pitch ends up being too high.

I would gamble on a 4 blade 16p as a good start, should be closer to what you want than what you have right now.

 

[LipschitzWrath]

Conventional wisdom goes with a 4 blade for good grab with a heavier style boat. Continuing that thought stream, 1 pitch down from what a 3 blade was getting to by way of RPM. The top speed will be down a bit but way less slip so good grab in the water. Sometimes too much grab if the pitch ends up being too high.

I would gamble on a 4 blade 16p as a good start, should be closer to what you want than what you have right now.

Mercury also took the time to listen to me and render a recommendation for a prop. Sounds like you and Mercury are on the same page - They are recommending a 15P Revolution 4 (4 blade SS). They said they would actually suggest a 16P, but they only make the Rev4 in odd pitches.

I'm definitely NOT afraid to go through this iterative process a couple times, especially if I can find a place that will do an exchange with me. However, I think that my dealer's idea of having me start at an 11P is a complete waste of time.

 

[LipschitzWrath]

Alright, just heard back from my dealer. He said, after speaking with Mercury, he is recommending a 15.5x15P Black Max if I want aluminum, or a 15x15P Enertia if I want stainless. I had already inquired with him about a Revolution 4 and he said those are "only for big block, higher power motors". That's not really what I've been led to believe, but whatever.

I am now currently waiting on pricing.

Does anyone have an opinion in light of this? Should I just trade him for the right pitch Black Max? Is the Enertia worth it? Or should I spring for the 4-blade Revolution?

 

[LipschitzWrath]

I'm just going to trade him straight across for the Black Max. If nothing else, I'll keep it as a spare when I upgrade later. He quoted me an exchange price of $647 to go to the Rev 4. He said the cost is the same for an Enertia, too. So, seeing as how I can buy a Rev 4 brand new with no exchange for a little over $500 elsewhere, I won't be taking him up on that.

The question still stands however - should I eventually upgrade to the Rev 4 or stick with the 3-blade Enertia?

Speaking of, can anyone recommend a good online site (nothing local) that sells Mercury propeller that will exchange props with me to make sure I get the right one?

 

[Maclin]

You kinda took the baton and ran right on past my level of expertise... I am sure some with more experience with those types of props will begin to contribute.

 

[LipschitzWrath]

Latest update - He decided that he wasn't as dedicated as he told me he would be in getting me a new prop in time to go out this weekend. So he has a new Black Max 15-1/2x15P that will be here next week sometime.

Because I was not blessed with patience as a virtue, I decided to jump online and order a 14-5/8" x 15P Revolution 4 stainless 4-blade, and have it expedited in time for this weekend. Cost me a pretty penny, but from everything I've read, I'm very excited. Plus it's supposed to be in the high 80's all weekend, so I want that holeshot for wakeboarding.

I'll report back with results on Monday (assuming I don't kill myself wakeboarding this weekend).

 

[theBrownskull]

I would think that the 15P stainless would fix your problems. I have a 17P 3 blade stainless on the same type of boat and it works great. I do not run at the higher altitudes though.