Low RPM's and looking for higher top speed

[zul]

Boat is new to me 2002 Rinker 232 cuddy and it's got a Bravo 3. Boat weighs 4,200 dry.
Most of my testing is w small to medium load (2 people, cooler and plenty of camp gear) full gas tank (75 gallon). This boat lives and runs @ 3,500ft of elevation, Lake Powell, AZ. It has a new 2021 long block.

4400rpm @ 39mph WOT. This 350 MAG EFI has 300HP and is rated for 4600-5000rpm.
3000rpm @ 23mph (lowest possible cruise while on plane and glassy water, trim down).

Current prop is a SS 4x4 Signature 14.5 inch and 22pitch. Prop is in good shape but has lost its shine/finish. Will a new prop with new shine improve preformance?

Small load, the hole shot is ok. Bow rise is high but comes down pretty quick. Large/full load and the hole shot was around 10-12 seconds to plane. About 50% of my boating is at full load. Is 10-12 a good hole shot when fully loaded?

1. Looking for better top end speed (2-3 mph would be great so I can barefoot waterski without wearing shoes). I don't go fast too often, but, well then, ya know?

2. Also thinking about hydro trim tabs for better fuel, help hole shot when loaded and extended, long run cruising. Should I re-prop 1st and hydro tab 2nd? Or install tabs 1st then re-prop? or forget the tabs?

Overall, it looks like the RPMs at WOT are too low? Maybe it was setup that way or the result of elevation 3,500ft? The trim up is also set pretty low, it only goes to 3/4 on the dash and no rooster at all (which is good to protect the outdrive). There is probably 1 mph in there if I re-set the trim limit ... a little bit??

Any prop suggestions? Maybe just leave it as it is? Are these test numbers good, acceptable or room to improve?

Thx Crew!!

 

[jimmbo]

Based on the Rpms, you need to go down in Pitch, by about 3 inches, or ditch one of the 4 blades, and then likely the required drop in Pitch will be less. Are Both Props the same Pitch, or are they staggered, also are both 4 blades or one a 4 and the other a 3?
I find the Holeshot on my 18 1/2 ft slow, as shown in this clip
View attachment MVI_0361.m4v

 

[Scott Danforth]

the 3500' elevation isnt helping. that is about a 10% reduction in power

make sure your throttle is fully open.

I agree, you need to go down in pitch or number of blades to get the engine RPM's up to where you are not lugging the motor

to bring your top speed up and your engine RPM's up, you need more power, which may mean more motor

your hole shot fully loaded isnt too bad. lower pitch will help the hole shot

However if you want all 3 - better hole shot, getting your RPM's into the correct range, and increase top speed. start looking at a bigger motor or a supercharger or look at making your boat smaller in weight and hull wetted surface.

 

[Texasmark]

Agreeing with Scott. You can't have your cake and eat it. Both conditions you want to achieve are opposite polarities.....i e, you have to sacrifice one to get the other. I'd say getting the RPMs up should be your goal and suffer a few MPH less than you are currently getting....unless you put in a larger engine.

 

[Texasmark]

Based on the Rpms, you need to go down in Pitch, by about 3 inches, or ditch one of the 4 blades, and then likely the required drop in Pitch will be less. Are Both Props the same Pitch, or are they staggered, also are both 4 blades or one a 4 and the other a 3?
I find the Holeshot on my 18 1/2 ft slow, as shown in this clip
View attachment 373171

Sloppy hole shot???? I don't think so. Looks pretty fast to me and MPH are right up there looking at your chine spray pattern and the distance of the transom convergence behind the boat. Looks like setup as in your picture, you have the best of both worlds.

 

[zul]

Currently, both blades are 4x4, slightly cupped and fully tarnished.

What affect does a 4x3 have on RPM, hole shot and top speed?
What affect does a 3x3 have on RPM, hole shot and top speed?

I think I know the answers to those questions, but what is the overall picture when switching to 3 blade? Would I invite some cavitation with 4x3? The Bravo 3 has me scratching my head and it invites so many more variables/choices/decisions. I'm feeling a bit underwater trying to understand the Bravo 3 and prop setup.

With 4400 RPM @ WOT, is that a small, medium or large problem for lugging the engine? I'd rather have a boat setup to protect the motor/drive than force minor gain of top speed. Seems like if I go with 19P I'd increase RPM by 200 but lose top end speed??

So, 19P 4x3 or 19P 3x3?

 

[zul]

You can't have your cake and eat it. Both conditions you want to achieve are opposite polarities....

Yep, I totally agree with that. I have opposite issues going on and maybe no way to solve them both. While getting stats from other identical boat owners, they are getting higher speed and higher RPM's. What gives? Maybe the 3500ft elevation is more than a 10% penalty?

Here are some copy and paste stats from others:

2000 Rinker Captiva 232 Cuddy
Engine:Merc 5.0
Outdrive: Alpha 1 (Gen2)
Prop: unknown
Speed: Top speed of 38-39mph on semi rough water, prolly could hit 40mph on a flat lake, this was at 4800ish RPM.
2000 Rinker 232 Captiva cuddy
350mag with Bravo3
On flat seas with 3/4 tank gas 2 people, my boat will hit 57mph with a gps
2004 Rinker 232 captiva cuddy with the 350 mag
26P bravo III. Top speed with 2 people and a half tank of gas is barely 40 mph at roughly 4600 RPM......this seems low to me....

These stats tell me that I should be getting higher RPM and higher speeds.
Something isn't right with the setup.

Next step is to trailer the rig to a lower elevation lake (350ft Lake Havasu) and do another batch of testing. Then we can see how much that high elevation is holding the boat back. It will take some time for me to get away for that test, tho.

 

[Scott Danforth]

you may not loose top end by dropping pitch or loosing a blade. the motor may be able to hit 4800 RPM which is better than lugging at 4400 RPM

 

[QBhoy]

Hi. Maybe I’m not reading this right. Have you the bravo 3 with twin props and both props are 4 bladed ?
Why ratio do you have ? Is it the normal 2-1 or close ?
I was very familiar with a maxum 2400 cuddy that had the 350 mag mpi and bravo 3. It had 26” original 3 bladed props. Would do just about 50 mph gps at around 5000 rpm. That’s as good as it gets for a boat like that with that set up really. Saw a claim of 57 mph quoted above. Not a chance.
When you say it’s the 350 efi…do you mean the mpi rather ? Big difference in power between the efi and mpi. Different rpm range too.

 

[jimmbo]

Sloppy hole shot???? I don't think so. Looks pretty fast to me and MPH are right up there looking at your chine spray pattern and the distance of the transom convergence behind the boat. Looks like setup as in your picture, you have the best of both worlds.

Still a lot slower than what my 2 Stroke Outboards did on the same OB version of the hull

here is a longer vid, with the outdrive trimmed out the whole time
View attachment MVI_0362.m4v

 

[jimmbo]

Yep, I totally agree with that. I have opposite issues going on and maybe no way to solve them both. While getting stats from other identical boat owners, they are getting higher speed and higher RPM's. What gives? Maybe the 3500ft elevation is more than a 10% penalty?

Here are some copy and paste stats from others:

2000 Rinker Captiva 232 Cuddy
Engine:Merc 5.0
Outdrive: Alpha 1 (Gen2)
Prop: unknown
Speed: Top speed of 38-39mph on semi rough water, prolly could hit 40mph on a flat lake, this was at 4800ish RPM.
2000 Rinker 232 Captiva cuddy
350mag with Bravo3
On flat seas with 3/4 tank gas 2 people, my boat will hit 57mph with a gps
2004 Rinker 232 captiva cuddy with the 350 mag
26P bravo III. Top speed with 2 people and a half tank of gas is barely 40 mph at roughly 4600 RPM......this seems low to me....

These stats tell me that I should be getting higher RPM and higher speeds.
Something isn't right with the setup.

Next step is to trailer the rig to a lower elevation lake (350ft Lake Havasu) and do another batch of testing. Then we can see how much that high elevation is holding the boat back. It will take some time for me to get away for that test, tho.

You mention 350 Mag, earlier in the list you say 5L, which is it?

 

[zul]

You mention 350 Mag, earlier in the list you say 5L, which is it?

My boat is:
350 Mag MPI, 300HP 5.7L
RPM Range is 4600-5000

The other boats and stats are from other people's boats, not identical to mine but similar. For comparison purposes.

Looks like I will try additional testing at lower elevation, then try a 20P prop. That should place me in the range around 4800 rpm's.

4x4 or 4x3 or 3x3 ?? That is the current and final question.

I am slow ... and slowly getting it. Thanks all!!

 

[QBhoy]

Based on the Rpms, you need to go down in Pitch, by about 3 inches, or ditch one of the 4 blades, and then likely the required drop in Pitch will be less. Are Both Props the same Pitch, or are they staggered, also are both 4 blades or one a 4 and the other a 3?
I find the Holeshot on my 18 1/2 ft slow, as shown in this clip
View attachment 373171

Looks sharp enough to me that ! Seeing some rpms right to the top there too or more. Looks propped well that jimmbo. My 18ft is terrible out the hole in comparison. Not much at first then everything after a certain rpm. Best it will do is 0-20 in about 5 seconds according to the smart craft. The outboard boat with a 3rd the power almost is quicker out the hole I think.

 

[Scott Danforth]

I would see if you can borrow a set of 3x3 21P or 3x3 22P

 

[zul]

Hi. Maybe I’m not reading this right. Have you the bravo 3 with twin props and both props are 4 bladed ?
Why ratio do you have ? Is it the normal 2-1 or close ?

When you say it’s the 350 efi…do you mean the mpi rather ? Big difference in power between the efi and mpi. Different rpm range too.

 

[zul]

It is MPI. Sorry, I listed that wrong.

 

[QBhoy]

It is MPI. Sorry, I listed that wrong.

No worries. You’re certainly lots down on pitch from that maxum I knew. But you may be at altitude perhaps. The 4 blades won’t be helping your performance top end at all though. That’s not the props it would have came with. Would have been twin 3 blade merc stainless props. Likely about 24-26” all things normal

 

[Texasmark]

Still a lot slower than what my 2 Stroke Outboards did on the same OB version of the hull

here is a longer vid, with the outdrive trimmed out the whole time
View attachment 373172

Ok bro. What's the difference in the HP of the two boats and transom area weights? Your wakes tell me that the 2 stroker had a lot more ponies and yes that did result in a super fast hole shot and 50+ MPH chine spray "fog" or faster.

No doubt the 2 storker was fast, give you that.

 

[Texasmark]

Currently, both blades are 4x4, slightly cupped and fully tarnished.

What affect does a 4x3 have on RPM, hole shot and top speed?
What affect does a 3x3 have on RPM, hole shot and top speed?

I think I know the answers to those questions, but what is the overall picture when switching to 3 blade? Would I invite some cavitation with 4x3? The Bravo 3 has me scratching my head and it invites so many more variables/choices/decisions. I'm feeling a bit underwater trying to understand the Bravo 3 and prop setup.

With 4400 RPM @ WOT, is that a small, medium or large problem for lugging the engine? I'd rather have a boat setup to protect the motor/drive than force minor gain of top speed. Seems like if I go with 19P I'd increase RPM by 200 but lose top end speed??

So, 19P 4x3 or 19P 3x3?

Carl Kiekhaefer originally used 2 blade props on his engines as the fewer the blades the higher the prop efficiency due to turbulence disturbances in the blade area caused by multiple blades as I read in historical records. So, theoretically, one should expect a drop in RPMs with the extra blade but realize better pushing of heavy loads....all other things equal..like brand, model, pitch, diameter, rake, cupping, blade thickness, type of material and all that.

All the Mercs in my boating arena back in the 50's and 60's were on light fast boats and if heavier dual installations with their 2 bladed props were the norm. Michigan wheel made brass 3 blade after market props that fit Mercs...I used one for water skiing but never saw one on another Merc...seems everybody just kept the OEM aluminum 2 blades. I never saw a tach on a boat in those days, all were fishermen and women, or Sunday fun seekers, but I wasn't in the racing circuit....just a kid out fishing or skiing and having some fun. So, best I can tell none of the folks in my boating circles had any idea as to what their engines were doing other than pushing their boats and there was no such thing as power trim and tilt!

Since vibration is out of sight on a single blade Carl equipped his engines with 2 blade props until he introduced the first 100 HP outboard, the Mark 1000 back in 1968, 2 stroke, with a change in paint color from Seafoam White to Phantom Black Lacquer and a 3 bladed prop. I assume that with an engine of that HP, he assumed it would be pushing large boats and needed more blade to water contact area. No history on this aspect.

So, with all that non essential blabbing, you should expect a drop in top speed and a faster hole shot if only the blade count was changed (increased) with identical props.

One thing is for sure: Everything is just speculation until you install a prop on your boat and put it through the paces for your boating habits and try different things like trim positions for a given function. Doing something as simple as getting the proper trim position can change a low speed "plower" (too much hull in the water) to a screamer!

On cavitation, that usually has to do with blade design and condition. If your props aren't dinged, any cavitation on your props would be caused by heavy corrosion generating tiny air bubbles around the rear tips of the blade....where the thrust isn't! Your question should address "ventilation" where the prop sucks in air from the environment due to the blade being too close to the surface. Ventilation can be observed when at higher speeds as the trim is increased, the prop will get closer to the surface and attempt to suck in ambient air. This is observed by a sudden increase in RPMs with an accompanying decrease in speed. Your SS props are probably high rake and cupped which probably wouldn't change all that much at high trim positions, but the extra blade could cost you a little extra slippage at a given throttle/trim setting.

I'm not an expert. Just a guy that had a boat when I was a teen back in 1956 and had one ever since.

 

[jimmbo]

The Outboard was 1998 150 FICHT on an 18 1/2 ft Glastron. It topped out a 54mph
The I/O is a 2002/2004 VP 5.7 260HP, on an 18 1/2 ft Glastron. It tops out at a bit over 60 with the Factory 2 bbl, about 6-7 mph more with the 4bbl. Holeshot was weaker with the 4 bbl due to an increase in Pitch to bring the rpms down to about 200 above the 4800 max spec.
Videos were shot with the 2bbl, about 16 yrs ago

I remember seeing a lot of Mercs with 2 Blade Props, they had a larger Diameter, and more Blade Area, than any 3 blade of the same Pitch. Few Merc Props were cupped until the very late 70s, when the Props went under a Serious makeover, with totally different Blade Shape, Rake, and Cupping, even on the AL Props, at the same time the Thrust Washer shape and Size also changed.