Hunter 44AC Boat Speed Under Power

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Jun 5, 2004
485
Hunter 44 Mystic, Ct
I was wondering if any other 44 owners could share their experience with boat speeds they can obtain while under power. I absolutely understand that there are many variables including prop, bottom condition, current, etc.

We have a 2005 44AC with a 4JH4E Yanmar (54/56HP). Max engine RPM is 3000 RPM per the nameplate. I have a fixed 3 blade prop that as I recall is 18 x 12 or 18 x 13. I can get up to about 3150 RPM at full throttle which would seem to indicate that the prop is sized correctly. Best speed that I can get is about 5.5 to 6.0 knots full throttle with a very small chop and little or no current. I'm in the neighborhood of 5 knots at 2900 RPM.

I was motoring alongside a friend last weekend and his Beneteau 393 passed me as though I was standing still. I always suspected that the boat was slow under power but it never bothered me until this season.

Marc
 

Alan

.
Jun 2, 2004
4,174
Hunter 35.5 LI, NY
When was the last time you had the bottom cleaned? If the engine and drive train are all functioning well I would guess that you are growing a colony of slime and critters under your boat. If I let my boats bottom go uncleaned for more than a couple of weeks it costs at least a knot of boat speed.
 
G

Guest

4JH

Hmmm, our 4JH2-TE has a maximum RPM of 4,250 driving a 18 X 15 fixed three blade. Your engine's RPM should be about the same. I've had our boat (1991 P32) up to nine knots under power, but seldom run it that hard. I normally operate it at around 2,000 RPM with a boat speed of seven knots. As Alan suggests bottom gunk could be slowing you down.

Terry Cox
 
Dec 19, 2006
5,809
Hunter 36 Punta Gorda
Not Right

Okay lets help find out whats wrong,being in CT I would think every year you haul for winter and clean the bottom so me thinks the bottom is not that bad to cause the problem.
My H-36 smaller Yanmar max rpm's are rated at 3600 and your's should be much more as stated by terry cox.
At the dock in neutral what is your max rpm's,that will tell you if the rpm's are different under power.
I have a sheet with all the Yanmar rated rpm's but it's on the boat and can't get to the boat until maybe later today or tomorrow morning,but I would check and compare the prop to other owners who have the same boat and what they are doing,check the owner list here and e-mail them and ask them what they have and compare.
My 2007 H-36 was doing around 6 knots and I was not happy with that,it seems other 356 / 36 hunters had different size prop than me and doing way more under power with less rpm's.
I did change the prop on the next winter haul and yes it is a Fex O Fold feathering three blade but also after talking to the tech at flex o fold they said my prop was not correct and we changed the pitch,it's now like night and day.
I not only get higher boat speed under power but she sails so much better under sail.
I would first see if you have the right prop and make sure you are getting full throttel at the dock in neutral,I will get back to you on the info I have on the boat later today or tomorrow.
Nick
 
Jun 5, 2004
485
Hunter 44 Mystic, Ct
I can get up to 3150 RPM under power transmission engaged but have not tried to see max RPMs in neutral. Either way shouldn't max RPM be limited to what is says on the Nameplate 3000 RPM regardless of whether or not I am in gear?

I did check the Yanmar spec sheet and it says :

Configuration 4-stroke, vertical, water cooled diesel engine
Maximum output at crankshaft * 39.6 kW (54 mhp) / 3000 rpm
Continuous rating output at crankshaft 36.0 kW (49 mhp) / 2907 rpm
 
Sep 15, 2006
22
Hunter 44 Shore Point Marina, Pine Beach NJ
We have a 2006 44 AC, under power at 2900 Rpm. SOG is 7.4 knots, the last 200 rpm will get it up to 7.8
 

Vinny

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Apr 6, 2006
343
Boat Less New Bern NC
Configuration 4-stroke, vertical, water cooled diesel engine
Maximum output at crankshaft * 39.6 kW (54 mhp) / 3000 rpm
Continuous rating output at crankshaft 36.0 kW (49 mhp) / 2907 rpm
Marc,

That is where the MAX HP is attained not the MAX RPM for the engine. 49 HP is produced at 2,900 RPM and the max of 54 HP is produced at 3,000 RPM. A 4JHE is about 3,400 MAX RPM and if you look at the Continuous numbers for your engine you will see that is 2907 RPM. 80% of 3,400 is only 2,720. But 80% of 3634 is 2,907 Which leads me to believe your 4JH4E's top RPM is 3,634 RPM. So the tachs being as accurate as they are run it at 2,900 RPM for the best overall performance and the proper loading of the engine. That being said if the prop is correct you should be able to get to the 3,600 range at full throttle in neutral and also under load. If you can't get there in neutral then there is something wrong such as valve clearance settings, dirty injectors, carbon build up or any number of other things. But if you can get there (or close) but can not when you are in gear you are over propped. Just because it (the prop) came from Hunter doesn't mean it is 100% correct.

Hope that clears some of it up.
 
Jun 5, 2004
485
Hunter 44 Mystic, Ct
Vinny

Thanks for the explanation. It seems to make sense. Two follow up questions: When the manufacturer quotes the continuous rating, is that always 80% of the max RPM? Also what do I do about the engine nameplate that I am pretty sure says Max RPM 3000, though after your explanation I am wondering if I misread it and it should be 3600. I'll check again this weekend.

Marc
 
Jun 5, 2004
485
Hunter 44 Mystic, Ct
Kurt

Would you happen to recall what size prop you have. Your performance is much better then mine and more in line with what my expectations would be.
 
Jun 4, 2004
73
Hunter 44 Keyport, NJ
Marc,

I have a 2005 H44AC with same engine as you, although I have a MaxProp. Like yours, my max engine RPM is quoted as 3000RPM which is lower than older Yanmars. I found that up to about 2500 RPM boat speed (in kts) under power is about RPM X 3/1000.

Example: 2000 RPM => 6.0kts
2400 RPM => 7.2kts

The relation starts to break down above about 2500 RPM when hull speed effects cut in.

Your reported speeds seem way low. Are you measuring your speed using the Raymarine knotmeter or a GPS? The knotmeter needs to be calibrated. The measured calibration factor on my knotmeter is about 1.3 and depends on how clean the transducer is.

BTW, under full sail, on a beam reach in 15-18 kts true wind my boat maxes out at about 8 kts, which is faster than I can go on power.
 

Vinny

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Apr 6, 2006
343
Boat Less New Bern NC
Vinny

Thanks for the explanation. It seems to make sense. Two follow up questions: When the manufacturer quotes the continuous rating, is that always 80% of the max RPM? Also what do I do about the engine nameplate that I am pretty sure says Max RPM 3000, though after your explanation I am wondering if I misread it and it should be 3600. I'll check again this weekend.

Marc
Mark,

I just went on line to check the engine specs and they are as you say. They are confusing at best. As far as the 80% rule most diesels run their best at 80% of their top RPM. The part that is hard to understand is it states that continuous operation is at 2,900 which would only leave 1,000 RPMs for emergency power. That doesnt make sense. I'll have to look into this more.
 
Jun 5, 2004
485
Hunter 44 Mystic, Ct
Larry

Thanks for the info. I am measuring the speed with the GPS. I can get simillar performance to yours while under sail but you are the second 44 owner that get's considerably better speed under power. I am starting to think that I have a prop issue with my fixed 3 blade prop.
 
May 8, 2004
101
Hunter 44DS Sea Cliff YC, NY
Have 2007 h44ds (same boat, different cabin top). Have standard 3 blade prop supplied by factory. With a clean bottom we can get about 7.5 kts at 2600 rpm, maybe 7.7 at 2800. Whatever the rating says, this is a comfortable range for long distance, good fuel economy. We also are on Long Island Sound. The water has plenty of marine life, and even with yearly bottom painting and hauling, cleaning the bottom makes a huge difference (I suspect at least as much because of a dirty prop as dirty bottom). We have a diver clean the bottom about every 4 weeks. Might do more if I raced it. We are cruisers, but no need to go slow.
 
Dec 2, 2003
1,637
Hunter 376 Warsash, England --
Marc,
I just ran the details of your boat and engine through 'Propcalc' available on the Castle Marine web site in Wales and it seems you need a 3 bladed prop which is 18.6" diameter and 15" pitch.
This should give you approx 8.5 knots at 2700 rpm.
The details of engine power and speed you quoted are correct as per the on line Yanmar data sheet for the saildrive version.
If you have standard shaft drive then a new calculation will be required.
Please remember that these calculations are normally only a starting point to get the prop right and often small improvements can be realised above what the calcs give.

Is this slow speed a new condition or has it always been like this?
 
Sep 15, 2006
22
Hunter 44 Shore Point Marina, Pine Beach NJ
I have the standard 3 blade prop the boat came with, I do not use the knot meter, I use the GPS to get ture boat speed, As Larry is refering to, the Knot meter need to calibrated.
 
Jun 5, 2004
485
Hunter 44 Mystic, Ct
Donalex

As best as I can recall, the boat has always been slow and nowhere near the performance that the other 44 owners are getting. The drive by the way is the standard shaft drive and not the saildrive. Weather permitting I'm going down to the boat this weekend and will attempt to get in the water to verify that I have the correct prop. I'll also check the bottom to make sure I don't have any significant growth on the bottom.
 
Sep 26, 2008
81
Hunter 44 Middle River, MD
I have a 2003 44AC. Max RPM= 4000. Three Blade Prop. At 2800 RPM I get 6.5 to 7.4 knots over ground (GPS) depending on the current.
 
Apr 22, 2001
497
Hunter 420 Norfolk, VA
Larry

Thanks for the info. I am measuring the speed with the GPS. I can get simillar performance to yours while under sail but you are the second 44 owner that get's considerably better speed under power. I am starting to think that I have a prop issue with my fixed 3 blade prop.
Marc, ... if, under sail, you are getting similar performance to other 44 owners w/ a "relatively" clean bottom; then your poor "under power" performance probably isn't caused by a fouled bottom.
I doubt that your OEM prop is at fault. Either your engine isn't delivering rated HP or (more likely) your transmission isn't converting it to proper shaft RPM.
I'd have a good Yanmar mechanic check the transmission and shaft RPM.
 

Vinny

.
Apr 6, 2006
343
Boat Less New Bern NC
I doubt that your OEM prop is at fault.
Buck,

No offense. But how can you say that? The props are NOT always the correct fit. If you think that the delivery of a unit off the line would be delayed for a week or so while the mistake of running out of the correct props gets corrected you are living in a different world.

I'm not saying that the prop is correct by no means but I wouldn't put it past a production manager to do what it takes to get the unit out either. I don't see how a transmission would be the culprit. If that is the case it is a bigger cover up than a prop. Does the drive train all come from the same place? Or are they matched up at the factory? I don't know that. But the easy thing to check is the prop.:)
 
Apr 22, 2001
497
Hunter 420 Norfolk, VA
Could be, Vinny .
But, I've been around ALOT of larger Hunters and I've never seen or heard of anyone w/ the wrong prop being deliver w/ a new boat.
I have, on the other hand, known Hunter owners to have had transmission problems (I'm one of them).
Maybe it IS the prop; but checking to see that at a given engine RPM, the shaft is turning at it's correct RPM is a fairly easy thing to ck.
 
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