Six Year Refit . . . Is 3.5 Knots Under Power Too Slow ?

[sabray]

So when was the bottom done last? I was really sad after doing mine that I waited so long. Performance is so much better.

[jrd22]

My last boat was 34', 13000lbs, 29' waterline with a 3GM30 engine. With a three blade Autoprop it would easily cruise at 6kts and exceed design hull speed at 3600rpm. We would do 3-3.5 kts at a fast idle. Something is wrong, but it doesn't sound like engine to me. You are getting proper rpm, your hull and prop are clean, sounds like you've dialed in the pitch properly. Someone else mentioned that your boat might be heavier than 13K (pretty light for 40'), is that possible? Either that or your GPS is kaput or the prop isn't working properly. I would try a different prop just for comparison.

[chala]

My boat is 14 tons 37 feet with a 30 hp Perkins, in fair weather at 2100 rpm the speed is around 5kts, 4kts with a 32kts head wind and boisterous sea. If everything is clean I can push it over 6kts but this is demanding too much of the machinery. It is really the water speed that is relevant and not SOG. You should be able to judge the water speed by passing bubbles in the wake. One of my first speedometers was just a teaspoon on a 3 meter string, the angle that the string does with the deck let me estimate the speed but real speedo is much better but need calibration to. Does the boat squat under power, watch the turbulence in the wake. One of the French baron Bic America Cup contender was so bad for drag turbulence than throwing an hat behind the boat, the hat followed the boat and the boat was scrapped.

[TaoJones]

After a six year refit, I think I'd learn to live with a vessel that could only power at half its theoretical hull speed . . . I'd just rename it s/v Half-Fast.

TaoJones

[Pete7]

Originally Posted by sabray

So when was the bottom done last? I was really sad after doing mine that I waited so long. Performance is so much better.

Agreed but also was the boats weight of 13000 lbs when it was in racing form and now after being gutted and rebuilt as a cruiser it weights a lot more perhaps? especially as the mast hasn't been fitted yet.

Having it lifted will give you the weight and a pressure wash at the same time would be good. Even a thin layer of slime will take a couple of knots off the top speed for us.


Pete

[Maxs]

The kanzaki tranmissions on some yanmars came with a Torque limiter coupling. It has some clutches and grease on the inside. If the torque is too much, or if they are simply old, it could be slipping. Check for an odd looking coupling. Same diameter as a standard, and about 2.5 inches in length.

[akio.kanemoto]

Wow!

Thank you for all the replies!!! Greatly appreciated!

OK, so I just came back home after a pretty interesting day both in and out of the water!

First off, I went for another dive and looked for funny things - which is quite a challenge since visibility is about one foot and the water was about 10degC (50degF).. nothing strange. I felt like a navy clearance diver... Checked prop angle again, nothing amiss.

Nothing snagged on the keel or rudder (rudder is also about 2m deep, so quite possible..) ... all good apart from being really cold (I wish I had a hood on my wetsuit!)

Fired up the engine and went for a lap, no joy, still same numbers.

I did check my email on my phone and read the earlier replies on CF and tried a few things including measured distances and observing the location of the bow wave at full speed. Using these other methods gave me different numbers! Also - the bow wave was roughly 3/4 of the way to the stern... something smells fishy.

OK, so back to the mooring, tie up, dry off, dinghy back to car, drive back, pack blah blah blah and drive to chandlery...

"Please give me that handheld GPS over there"...

$424 later and armed with a Garmin GPSMAP 78stc, drive back home, pick up dinghy, drive to boat ramp blah blah blah...

Lo and behold! It turns out that the mounted Maretron GPS unit twice the price of the handheld unit displays almost EXACTLY HALF the speed of the handheld!!!! Bizarre!!!

So hitting the maximum throttle-stop and at 3000 rpm, I managed 7.4 knots under power today according to the handheld.. WOOHOO!!! Big sigh of relief!!!

Now considering that the Maretron GPS has no real configurable settings or calibration etc and the display is using the right units etc - what on earth is with this half speed business!?!?

Thank you all again, I can finally have a good night of sleep!!!

[MarkJ]

Originally Posted by akio.kanemoto

I managed 7.4 knots under power today according to the handheld.. WOOHOO!!!

Congratulations!!!!!!!!!!!!!!!!!!!!!


The GPS is set to a moving average speed.

Can be a real pain. There will be another speed option to look at.





Mark

[akio.kanemoto]

Originally Posted by MarkJ

Congratulations!!!!!!!!!!!!!!!!!!!!!


The GPS is set to a moving average speed.

Can be a real pain. There will be another speed option to look at.





Mark

Thanks! Admittedly, this was really hammering the engine though.. it didn't like being pushed that hard! It sounds much happier at approx 2000 rpm and 5-5.5 knots.

As for moving average - I'll look into this, but even after a minute or so of running at the same speeds, the display didn't change.

At least I've got an electronic problem now and not a catastrophic "bad hull" or other "cruise stopping" problem!

Only a few months to go!!!

[MarkJ]

Originally Posted by akio.kanemoto

It sounds much happier at approx 2000 rpm and 5-5.5 knots.

Thats the speed I run at. Fuel consumption is vastly better.

I normally run at 4.5 to 5 knots at 1,800 rpm on a 56hp, and try to get a bit of rag up to help out.

people who motor past you at 7 knots are next seen at the fuel wharf!


Mark

[Unicorn Dreams]

Good deal

[MarkJ]

I'm just kinda figuring what it must be like to go through a 6 year refit and then only see 3 knots on the screen.

LOL




I'll be you were so pleased to see the 7.4 knots



Mark

[Jim Cate]

G'Day Akio,

Hah! A good outcome for you, except for the odd GPS readings. Do the positions recorded by the two units agree? How about COG? Just curious...

Incidentally, where do you keep the boat?

Cheers,

Jim

[akio.kanemoto]

Originally Posted by MarkJ

I'm just kinda figuring what it must be like to go through a 6 year refit and then only see 3 knots on the screen.

LOL




I'll be you were so pleased to see the 7.4 knots



Mark

G'day,

I can't begin to tell you the overwhelming "sinking feeling" I had when I couldn't push past the 3 knots.. I've had so many challenges these past 6 years when stuff didn't work or I had to rebuild something that I had just finished glassing etc... or reinstalling and buying something else when something didn't work as expected (12V Duoetto water heater.. ahem..).. but all these other problems were just "minor depression", since they could be solved with either money or time. But the 3 knots looked like a fundamental design issue...

So my relief is commensurately phenomenal too!

So I've just got to get the mast back in (rigger has been saying "next week" for about 3 months now...) and then start doing some sea trials.

The last of the fabrication work ends in about 2 weeks, I'm just missing the galley sink and sump, so we're ready to move aboard.

I just wish the house would sell soon!

[akio.kanemoto]

Originally Posted by Jim Cate

G'Day Akio,

Hah! A good outcome for you, except for the odd GPS readings. Do the positions recorded by the two units agree? How about COG? Just curious...

Incidentally, where do you keep the boat?

Cheers,

Jim

Yes, the positions reported agree. (I didnt look at exact LAT/LON numbers, but the handheld has a map on it and it shows my location correctly, as does Maxsea TZ, which received the Maretron GPS200 output.

As for where we are - we'll be moving to where you were very shortly. Pittwater.