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03-12-2024, 07:09
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#16
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Registered User
Join Date: Aug 2016
Location: Long Island, NY
Boat: Cal 33-2
Posts: 507
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Re: Unable to motor at proper speed
This sounds like a problem with the pitch of the prop being low. You have gotten some good advice to verify the transmission ratio and then contact Flexofold. You state that you do not know the pitch of the installed prop. Not sure about Flexofold, but most props have the diameter and pitch stamped on the prop somewhere. Assume you have been hauled for the season so examine the prop carefully to see if you can find the pitch stamped on the prop. Flexofold may be able to help in determining the current pitch. If the pitch is off based on talking to Flexofold, you may be able to just get a new set of blades versus an entirely new prop.
FWIW my boat (Cal 33-2) is similar in size to yours with a Yanmar 3GM30F and a 16 inch 2-blade folding prop. I can easily do 6 knots at about 1/2 throttle.
__________________
S/V First Tracks
1985 Cal 33-2
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03-12-2024, 07:45
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#17
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 7,168
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Re: Unable to motor at proper speed
I think you are expecting way to much from a 21 hp engine for your size boat. While displacement is a factor, so too are many other things, ie, LWL, etc, etc.
You can fool around with the prop all you want, but as long as the hp stays the same, you'll see little to no improvements and around 5 knots for your boat with that engine sounds about right.
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03-12-2024, 07:57
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#18
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Registered User
Join Date: Aug 2016
Location: Long Island, NY
Boat: Cal 33-2
Posts: 507
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Re: Unable to motor at proper speed
OP reports that others on the 349 forum with same engine report better powering speeds than he is getting. So I would continue to pursue this.
__________________
S/V First Tracks
1985 Cal 33-2
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03-12-2024, 08:27
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#19
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 7,168
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Re: Unable to motor at proper speed
Years ago, my first boat had a relatively small engine (17 hp) for it's size (around 38'). I tried all sorts of things to improve performance to no avail and around 5 knots was the best speed I could attain.
Some years later that engine got yanked out and replacement with a 27 hp engine and also a slightly large prop. One would think that the difference between 17 and 27 hp would have shown a marked improvement, but it did not and my cruising speed remained at around 5 knots.
Below hull speed of a sailboat, it appears that not much hp is required to get the boat moving, and the only advantage the 27 hp engine had was in rougher weather, where the bigger prop had more bite on the water.
To get my boat up to hull speed would have required an engine in the 35 hp range, and even so, that engine would have to work hard to do it, meaning an engine in the 45 hp range would be more appropriate.
I've done much research on the topic and much playing around with engines, props and the like, and it's a complicated process to get everything just right, but at the end of the day, without adequate hp, you'll not get far.
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03-12-2024, 08:38
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#20
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Registered User
Join Date: Jan 2024
Location: Latvia
Boat: Scanmar 35
Posts: 32
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Re: Unable to motor at proper speed
I have similar problem as OP. On my 35 foot boat with 10,582.00 lbs (4,800 kg) displacement I also can achieve only around 5 knots. Although my boat is even a bit lighter and I have a bit stronger engine Yanmar 3YM30 (29 HP). By boat also has Flexofold propeller (2 blades, 16 inches, unknown pitch). As I can't install bigger propeller due to blades proximity to hull I would suspect the pitch is not right.
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03-12-2024, 09:15
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#21
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Registered User
Join Date: Dec 2010
Location: Oregon
Boat: Beneteau/343
Posts: 373
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Re: Unable to motor at proper speed
Quote:
Originally Posted by sagablu
The bottom was clean when the boat went in the water, plus I cleaned it, and I had a professional diver clean at one time. Except for a barnacle on the strut and a few on the prop, the bottom was mostly clean. Regardless, the before and after results were the same. The problem lies elsewhere
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Oh well, I always hope for an easy answer first.
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03-12-2024, 10:01
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#22
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Registered User
Join Date: Feb 2016
Location: Northport NY
Boat: Pearson 10M
Posts: 470
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Re: Unable to motor at proper speed
Quote:
Originally Posted by davefromoregon
Oh well, I always hope for an easy answer first.
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I believe history will show that no boat related problem since the beginning of time was ever easy. We keep hoping though!
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03-12-2024, 10:19
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#23
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 7,168
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Re: Unable to motor at proper speed
Well, it's like this, no amount of engine tuning will get a 1600cc VW engine to perform like a supercharged 6.2 litre V8.
Simply won't happen.
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03-12-2024, 10:36
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#24
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Registered User
Join Date: Feb 2016
Location: Northport NY
Boat: Pearson 10M
Posts: 470
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Re: Unable to motor at proper speed
Quote:
Originally Posted by MicHughV
Well, it's like this, no amount of engine tuning will get a 1600cc VW engine to perform like a supercharged 6.2 litre V8.
Simply won't happen.
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Blow is a chart showing the motoring speed of the exact same boat with a flexifold propeller. This was posted on the Jeanneau 349 forum. There are others with the same results. I'm not expecting the impossible, I'm expecting and would be happy with an average result. I'm just not getting it, trying to find out why.
RPM / SOG
1400 / 4.8 kt
1600 / 5.2 kt
1800 / 5.6 kt
2000 / 5.9 kt
2200 / 6.2 kt
2400 / 6.5 kt
2600 / 6.8 kt
2800 / 7.0 kt
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03-12-2024, 11:48
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#25
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Registered User
Join Date: Aug 2021
Location: PNW
Boat: 35 Ft. cutter, custom
Posts: 2,952
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Re: Unable to motor at proper speed
Ok, you've already stated that bottom and prop are clean.
I go back to my first post, it's either pitch, diameter, or blade area, or some combination of them.
Roughly speaking, 1" of diameter is equal to ~2" of pitch and given the choice the addition of diameter is more efficient than adding pitch.
With that style prop adding blade area is probably not going to happen.
In forward gear, if you hit max rpm before the gas pedal hits the floorboard you know the engine is not seeing the load it should, (we assume the tach is correct).
__________________
Beginning to Prepare to Commence
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03-12-2024, 12:37
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#26
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Registered User
Join Date: Feb 2016
Location: Northport NY
Boat: Pearson 10M
Posts: 470
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Re: Unable to motor at proper speed
Quote:
Originally Posted by Bowdrie
Ok, you've already stated that bottom and prop are clean.
I go back to my first post, it's either pitch, diameter, or blade area, or some combination of them.
Roughly speaking, 1" of diameter is equal to ~2" of pitch and given the choice the addition of diameter is more efficient than adding pitch.
With that style prop adding blade area is probably not going to happen.
In forward gear, if you hit max rpm before the gas pedal hits the floorboard you know the engine is not seeing the load it should, (we assume the tach is correct). 
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Understood, this is helpful. I did speak with one of the US distributors of flexifold, he is contacting the mothership in Denmark and will let me know what their thoughts are. I just have to get the transmission ratio confirmed. Thank you for your help.
Problem is that I won't know if any changes I make will work until the boat's back of the water, late part of April.
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03-12-2024, 17:58
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#27
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Registered User
Join Date: Jun 2011
Location: Caribbean
Boat: Hylas 46
Posts: 714
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Re: Unable to motor at proper speed
Quote:
Originally Posted by sagablu
I have a 2018 Jeanneau Sub Odyssey 349, 34 ft (10.5m) and 12,000 lbs, (5390kg). The prop is a 15" Flexofold 3 blade that I assume was the factory prop. I am unsure of the pitch. The motor is a yanmar 3YM20, 21hp. The problem I am having is I am unable to attain the speed that I expect from the boat and from what I hear should be expected. I've been reading the Jeanneau 349 Forum, and I understand that seven knots at full throttle is to be expected. Under no circumstances can I get more than five no matter what I try, regardless of wind and tide. It appears that others have the same prop and I am at a loss. Reading the conversation someone else with the same boat had with Flexofold, The specification was a 16-in two blade, not
the 15 in three blade. The conversation went on to say that a 16-in three blade would provide more thrust but might not allow the motor to hit Max RPM. I can currently easily hit Max RPM.
Of course, the bottom is clean. I checked the prop in and out of the water, it seems to open and close without any restriction
The funny thing is a review I found did a test of folding props and Flexofold came out on top. Totally not understanding what's happening.
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It would be very helpful to everyone (you, us, any "prop guy" you talk to) to know the pitch of the current prop. How else can you quantify the difference between the current, "under-performing" prop and a proposed new one?
I know you said a couple of times that the hull and prop were clean, but just be clear, neither is clean in the pictures shown in the first post. Especially the prop. It can't be overemphasized how important a clean prop is. Any attached growth or remnants increase rotational resistance (waste power), reduce lift (thrust) and increase cavitation.
Quote:
Originally Posted by sagablu
Blow is a chart showing the motoring speed of the exact same boat with a flexifold propeller. This was posted on the Jeanneau 349 forum. There are others with the same results. I'm not expecting the impossible, I'm expecting and would be happy with an average result. I'm just not getting it, trying to find out why.
RPM / SOG
1400 / 4.8 kt
1600 / 5.2 kt
1800 / 5.6 kt
2000 / 5.9 kt
2200 / 6.2 kt
2400 / 6.5 kt
2600 / 6.8 kt
2800 / 7.0 kt
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That may be data from the same boat and make of prop, but it's not from the same engine. (And therefore, probably not the same size prop you need.) Your Yanmar should rev up to 3600 rpm, whereas this one only goes to 2800 rpm. Did they re-power? Say, with a Beta 35 (i.e. 35 hp)?
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03-12-2024, 19:11
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#28
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Registered User
Join Date: Oct 2015
Location: Chesapeake Bay
Boat: FP Mahe 36 Duo
Posts: 59
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Re: Unable to motor at proper speed
Just a question regarding boat history. Do you know if the sail drive has ever been replaced? Ran into an interesting situation several months back where a customer took his boat in regarding a saildrive issue. The repair facility told the customer his saildrive was shot. They replaced the saildrive and the boat lost almost 2 knots of speed! The customer was enroute and had no time to litigate or investigate the issue. So he goes on his way after an approximate 16K repair bill and almost 2 knots slower boat speed. Clearly the shop introduced a saildrive with a different gear ratio. Excess and slow moving inventory likely. What an opportunity when servicing someone enroute right? I’m not saying that’s happened to your yacht but the loss of speed you’re talking about; particularly at max rpm, and considering all other conditions the same, is more than peculiar. There’s a lot that goes into boat speed. Of course the obvious; hull and running gear cleanliness. But the key here is that you haven’t changed the prop and the boat makes rpm. Sometimes the problem is not so obvious. Good luck. There’s some chicken on that bone for sure……
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03-12-2024, 19:27
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#29
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,991
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Re: Unable to motor at proper speed
Quote:
Originally Posted by Kazamaran
Just a question regarding boat history. Do you know if the sail drive has ever been replaced? Ran into an interesting situation several months back where a customer took his boat in regarding a saildrive issue. The repair facility told the customer his saildrive was shot. They replaced the saildrive and the boat lost almost 2 knots of speed! The customer was enroute and had no time to litigate or investigate the issue. So he goes on his way after an approximate 16K repair bill and almost 2 knots slower boat speed. Clearly the shop introduced a saildrive with a different gear ratio. Excess and slow moving inventory likely. What an opportunity when servicing someone enroute right? I’m not saying that’s happened to your yacht but the loss of speed you’re talking about; particularly at max rpm, and considering all other conditions the same, is more than peculiar. There’s a lot that goes into boat speed. Of course the obvious; hull and running gear cleanliness. But the key here is that you haven’t changed the prop and the boat makes rpm. Sometimes the problem is not so obvious. Good luck. There’s some chicken on that bone for sure……
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Good thought, but it would need to have been a transmission replacement, as the SO349 is shaft drive, not a saildrive.
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03-12-2024, 20:19
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#30
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Moderator
Join Date: Feb 2010
Location: Australia
Posts: 3,942
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Re: Unable to motor at proper speed
Quote:
Originally Posted by Kazamaran
Just a question regarding boat history. Do you know if the sail drive has ever been replaced? Ran into an interesting situation several months back where a customer took his boat in regarding a saildrive issue. The repair facility told the customer his saildrive was shot. They replaced the saildrive and the boat lost almost 2 knots of speed! The customer was enroute and had no time to litigate or investigate the issue. So he goes on his way after an approximate 16K repair bill and almost 2 knots slower boat speed. Clearly the shop introduced a saildrive with a different gear ratio. Excess and slow moving inventory likely. What an opportunity when servicing someone enroute right? I’m not saying that’s happened to your yacht but the loss of speed you’re talking about; particularly at max rpm, and considering all other conditions the same, is more than peculiar. There’s a lot that goes into boat speed. Of course the obvious; hull and running gear cleanliness. But the key here is that you haven’t changed the prop and the boat makes rpm. Sometimes the problem is not so obvious. Good luck. There’s some chicken on that bone for sure……
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A $16,000 repair on a saildrive sounds barely believable, a new yanmar saildrive is around $AUS 6,000 and 4 hours labour to change it. Since the ratios are fairly static on the ones that I’m most familiar with, I’m interested to know what brand of saildrive? was installed to replace…. what brand and model of saildrive?, if you can give me that info, I’ll do my own search through the service manuals.
Did you hear this story at a marina bar or is it credible information. What’s likely is that the original propeller was slipping on the rubber hub and was transferred to the new saildrive.
The OP’s boat has a shaft drive with a reversing gearbox.
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