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Old 11-06-2014, 12:54 PM   #1
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Island Packet PY Cruiser sea trial

I recently had a PY Cruiser surveyed, and on the sea trial the speeds at different RPMs were quite a bit slower than what I expected after reading this data from a test done back in 2008:
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The full article is here.
Island Packet PY 41

We were only able to get 7.8 knots at WOT of 3200, and about 6 knots at 2600 rpm. When I plug the boat's data into the boatdiesel calculator it shows a theoretical hull speed of 7.8 knots using the following inputs:

displacement hull, 23000 lbs displacement, 35' LWL, 4JH4-HTE Yanmar 109hp (500 hours) at 3200 rpm , 2.63-1 trans ratio. 21X16 three blade prop.

The calculator figures 46 hp at 2400 rpm needed to get to the 7.8 knots, but like I said we needed 3200 to get there. This Yanmar supposedly makes about 46 hp at 2400 rpm.

Is there a logical explanation for needing full power to reach hull speed?

The bottom had a little growth but not much. We were in calm water. Not much wind.

We were more heavily loaded than the boat in the test article by about 2000 lbs.

Could our hand held GPS have been that far off? The GPS on the boat was inop at the time.
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Old 11-06-2014, 01:50 PM   #2
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Cardude,
The numbers you recorded seem real. The numbers from the test article seem very optimistic for a 23,000 lb boat. In the article they do say the boat had a super clean bottom and the water & fuel tanks levels were almost empty. 10 lbs of gear. And perhaps they were running with the tide to achieve 10.9 knots. (and the tide turned for their return journey)

I don't see how a 110 hp engine can push a 23,000 lb boat that much above theoretical hull speed unless it is shaped like a rowing skiff.

btw - IP still do make a nice boat, even if they don't obtain miraculous speeds.
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Old 11-06-2014, 02:00 PM   #3
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Hmmm, you did reach 3200 which is the WOT spec, so that's a good thing, I agree with AusCan the boat test numbers look very ambitious.
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Old 11-06-2014, 02:20 PM   #4
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Well you were 600 rpm off of Max. That right there indicates some issue/s.

Then there is the obvious fact that the boat review seatrial was done with very light loads.
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Old 11-06-2014, 02:27 PM   #5
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Bill I could be wrong, but on the Yanmar website showed 3200 max which is what he got.
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Well you were 600 rpm off of Max. That right there indicates some issue/s.

Then there is the obvious fact that the boat review seatrial was done with very light loads.
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Old 11-06-2014, 03:01 PM   #6
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Well you were 600 rpm off of Max. That right there indicates some issue/s.

Then there is the obvious fact that the boat review seatrial was done with very light loads.
The boat test was done with a Yanmar 4JH3-HTE which is rated at 3800 rpm with a 3.0:1 reduction gear. The boat being discussed is powered by a newer 4JH4-HTE which is rated at 3200 rpm with a 2.63:1 reduction gear.

That explains the 600 rpm, but how about the difference in observed speeds? Where did the 3.1 knots go?
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Old 11-06-2014, 03:04 PM   #7
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The max rpm of that 4JH4-HTE is 3200, the way I read it. Yes, the boat in the test was the 4JH3 which makes a bit more HP but at 600 higher RPM.

Any ideas why I need the full 109 HP to get to hull speed and not 46HP? Is there a possibility the engine is not making full power at 3200 RPM? If the turbo is not working would it get up to 3200RPM? There was no abnormal smoke noted.
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Old 11-06-2014, 03:11 PM   #8
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Bill I could be wrong, but on the Yanmar website showed 3200 max which is what he got.
Ah yes, I was looking at the spec for the wrong engine model. Never mind.
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Old 11-06-2014, 03:21 PM   #9
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Are you sure that you had the 110 hp engine? Older Yanmar 4JH3HTE engines topped out at 3,800 rpm and what you may have is the older 100 hp, version. That is what was tested in the referenced PMY article.

That would explain most of your observations. The engine was only putting out maybe 70 hp at 3,200 because the bottom was a little dirty and maybe it was a little overpropped.

Your boat could easily have been loaded to 28,000 lbs which should require 40-50 hp to hit hull speed. If your engine was really producing 70 hp then a dirty bottom or prop could explain the difference. My neighbor has that same engine in his 50,000 lb IP 485 and it pushes that boat to its hull speed.

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Old 11-06-2014, 03:31 PM   #10
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The max rpm of that 4JH4-HTE is 3200, the way I read it. Yes, the boat in the test was the 4JH3 which makes a bit more HP but at 600 higher RPM.

Any ideas why I need the full 109 HP to get to hull speed and not 46HP? Is there a possibility the engine is not making full power at 3200 RPM? If the turbo is not working would it get up to 3200RPM? There was no abnormal smoke noted.
One simple test would be to check the 'high idle' (max rpm in neutral) which should be 3775 +25 -75 rpm. If lower than 3700 rpm, check throttle cable for full travel and check for clogged fuel filters.

With a 21x16 prop, at 7.8 knots that boat requires less than 50shp. If that is all you get at 3200 rpm, then there is something wrong. The Boatdiesel prop calculator indicates a 21x17 prop so in a perfect world, you would actually have a WOT a bit higher than 3200 rpm at 7.8 knots.

At this point, if you are serious about the boat, I would invest in a thorough mechanical survey by reputable Yanmar specialist. Way too much at stake here.
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Old 11-06-2014, 03:44 PM   #11
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Are you sure that you had the 110 hp engine? Older Yanmar 4JH3HTE engines topped out at 3,800 rpm and what you may have is the older 100 hp, version. That is what was tested in the referenced PMY article.

That would explain most of your observations. The engine was only putting out maybe 70 hp at 3,200 because the bottom was a little dirty and maybe it was a little overpropped.

Your boat could easily have been loaded to 28,000 lbs which should require 40-50 hp to hit hull speed. If your engine was really producing 70 hp then a dirty bottom or prop could explain the difference. My neighbor has that same engine in his 50,000 lb IP 485 and it pushes that boat to its hull speed.

David
Wow, that would be something. Just got off the phone with the surveyor and compared notes. He said he got that model number right off the engine so I'm sure we have the right engine and not the 4Jh3, unless the engine was mis-tagged? Does that ever happen?

The only other explanation I can think of is maybe the GPS app on our iphones were off a bit? If they were off by 1 knot that would probably explain things.

The surveyor reinforced my recollection of no black smoke, no current and not much wind. He did bring up the fact that the tach seemed a bit off at idle (200 rpm), and he could not get to the front of the engine to check it with his hand held tach. Would 200 rpm make the difference?
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Old 11-06-2014, 03:48 PM   #12
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I would never trust a yanmar tach (was it a Yanmar panel) they are notorious for being off, phototach is the only way to go and that could lead to some of the issue along with bottom condition.
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Old 11-06-2014, 04:33 PM   #13
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I would never trust a yanmar tach (was it a Yanmar panel) they are notorious for being off, phototach is the only way to go and that could lead to some of the issue along with bottom condition.
All of the later style (grey) instrument panels with rectangular connectors have VDO tachs and sensors. It seems they are calibrated by the factory to read about 150 rpm too high. I'm not sure why this is the case, but it is well known. Here is a chart that gives the 'high idle' speeds for some common Yanmar engines and shows this difference. When conducting tests for WOT or High Idle, it is preferred to use a digital handheld tach, but if not available, at least subtract 150 rpm from the Yanmar tach to estimate true engine speed. At lower engine speeds this difference is less.

Now, if you only observed 3200 rpm on the sea trial, you were likely only making 3050 rpm . . . . . this is moving the wrong way. Again, time for a pro. Very cheap insurance.

Good luck in solving your mystery. . . .

BTW here is an excerpt from the Yanmar factory shop manual with the proper specs:
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Old 11-06-2014, 04:42 PM   #14
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I agree on the engine survey. I did an oil sample and it came back fine but now I'm confused.

Thanks.
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Old 11-06-2014, 05:17 PM   #15
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I agree on the engine survey. I did an oil sample and it came back fine but now I'm confused.

Thanks.
I agree with you. I just re-read the review and if it was at all factual, I would definitely have questions for the seller or broker as it relates to the performance you observed vs. the review. Just an honest, heart to heart asking them to explain the missing 3 knots. That's a huge difference, and would definitely be a deal breaker for me, particularly at the price of these boats.

I would also try to contact Island Packet Yachts and ask someone in sales, service etc. The same basic boat is still in production as the SP Cruiser MK 2. It has the same power and their website still claims:

"With calm seas and light winds we reported an 850 NM range at a cruise speed of 8.3 knots and nearly a 700 NM range at 9.1 knots. And if you dial her back to a sedate 7.3 knots, running efficiency hits a wallet-warming 16.8 mpg, with a range of nearly 3,000 nautical miles. - Power & Motor Yacht"

So . . . . . I think somebody's got some 'splainin' to do!
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Old 11-06-2014, 06:04 PM   #16
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As Larry said, check the high idle rpm with a phototach. That will tell you which engine you have and remove that question. The 100 hp 4JH3HTE should hit 4,000 rpm or better with no load and the 110 hp 4JH4HTE should only hit 3,400 rpm or so.

David
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Old 11-06-2014, 06:18 PM   #17
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I'd guess a combination of all the things mentioned above. That's a pretty steep prop for 21", btw.. I'd expect a larger diameter and less pitch. But since it is "spec" for the boat, subtract a bit for a dirty bottom, maybe a dirty prop, maybe a bit of RPM missing, maybe a bit off on your GPS, tach, add 2000 lbs,,.... 3 knots (if indeed it is that) may not be out of reach for the perfect boat.

With a new bottom and near zero in my water and fuel tanks, I can reach 9.4 knots in my fat Manatee at about 3650 RPM with a similar 140 HP Yanmar. Six weeks ago I left Stuart for Indiantown on the Okeechobee Waterway. It would still turn 3600, but with a year-old filthy dirty bottom and running gear, maybe 50 gallons of water and 200 of fuel, the best I could do was 7.8 WOT.

The IP PY Cruiser is still a heck of a boat.
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Old 11-06-2014, 06:49 PM   #18
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Larry

Thanks for that comparison-- that makes me feel better about it. I tested my phone GPS app a few minutes ago and it was off 1 mph from my son's app, so that could be part of the problem.

The prop was clean but the bottom had growth-- I should have had it power washed.

I called IP Yachts and a sales guy said the boat is capable of 10 knots if all the stars are aligned, but most run it at around 7 knots.

That test boat in the article had the 4JH3-HTE engine in it that makes 100 hp at 3800 rpm and a 3:1 trans ratio I just realized. Maybe that helps explain the difference in the top speed?
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Old 11-06-2014, 07:58 PM   #19
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A few simple points some already made. Sea trail rpms are useless unless verified by photo timing. You can still photo time and go back to sea trail #s and correct. Anybody doing a sea trail without photo timing and correcting inst. should not be doing it due to a complete lack of understanding. Next, boat obesity can account for a good deal of performance variation between what is often light new boat data vs. 2 year old boat. A dirty bottom or prop problem also has to be excluded. If your engine does not get 100% + rated rpm at WOT you are over propped unless there is another problem you can correct such as a very dirty bottom or fouled prop but a real sea trail assumes those things are taken care of prior to trail.
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Old 11-06-2014, 09:00 PM   #20
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Absolutely correct regarding the sea trial rpms. They must be corrected to be meaningful.

Now, I hate to throw in another variable, but since you questioned the accuracy of the GPS speeds you observed, it might be helpful to re-run the WOT test under more controlled conditions:

Try for protected, smooth water and minimal current.

1. Run a 2-way measured distance between two fixed points. Channel markers are good for this because they are stationary and their distances can be measured on a chart or plotter. The course must be straight and you need to steer as accurately as possible using as little rudder correction as you can. A mile is a good distance and some bodies of water even have a measured mile distance between some marks just for this purpose. Start each pass at maximum speed and rpm. Observe the time and record. Turn around and re-run in the opposite direction, again at maximum speed and rpm. Observe the time and record. Calculate the speed for each pass, average the two and you have your true speed through water. This is time-consuming and tedious, but it gives very accurate results.

2. Alternatively, a 2-way trial long enough for the speed to stabilize with speed measured by GPS. And again, average the readings for your speed.

You suggested that you thought your GPS was reading slow. While I have never seen this before, the first method will eliminate that possibility.

Finally, you asked "That test boat in the article had the 4JH3-HTE engine in it that makes 100 hp at 3800 rpm and a 3:1 trans ratio I just realized. Maybe that helps explain the difference in the top speed?"

I think not. The boat your are looking at has a 4JH4-HTE which is rated at 110 hp at 3200. Due to the different gear ratios, the shaft rpm difference is only 50 rpm, so the propellers should be very close. With more power, I can't imagine any scenario in which it would result in lower speeds.

Keep us posted on your progress. This one is pretty interesting..
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