• From: Manchester, England
  • Registered: 2005-10-04
  • Posts: 59

Topic: Hull Speed

I've now got the boat back in the water after the winter works and the the hull and 13" 3 blade prop all cleaned and antifouled, the 2GM20 engine was taken out and new engine bearers put in and it sounds to be running fairly sweetly, so took for a spin in the marina today and at top speed reached 4.6 knots (this was with a slightly shortly waterline as all the anchor chain is out at the moment and the anchor is not in place so it's a bit back heavu and the bow waterline is about 6" above the real waterline at the moment).

4.4 knots is OK but is that the average or do other boats get more or less ?

Cheers
Andrew

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If the memories are better than the dreams then it's all over.....
[url=http://www.contessa26moonshine.me.uk]www.contessa26moonshine.me.uk[/url]

eebygumcaptain's Website

  • From: Victoria, BC
  • Registered: 2005-05-21
  • Posts: 47

Re: Hull Speed

That seems super slower especially given the engine you have in there.  I cruise at 5.1 knots with a 1gm10.  If I crank the RPM's up I can go about 5.6 knots.  What RPM can you reach at full speed?  Sounds like to me that you have a prop issue.  I would think with the proper prop you should be able to make hull speed (about 6 knots) without too much trouble.

Mark Sherlock's Website

  • From: Victoria B.C.
  • Registered: 2006-03-11
  • Posts: 171

Re: Hull Speed

With the farryman  7 H.P.The one time I checked I was cruising at 4+ knots on flat water,no tide and a not perfectly clean bottom.You should be able to get close to six knots  with that much power,but that is strictly just my opinion.

4 Reply by eebygumcaptain (edited by eebygumcaptain 2006-03-19 14:43:11)

  • From: Manchester, England
  • Registered: 2005-10-04
  • Posts: 59

Re: Hull Speed

Unfortunately I don't have a rev  counter so not sure of the RPM but at full tilt it was doing about 4.6 in the marina.

Not sure if it's a prop issue but as posted before the gap between the tip of the prop and the hull is only about a quarter  of an inch (yep that's right ..... about 4-5 mm)  and the marine engineer who put the engine back in thought this may cause caviatation ? the 13" prop is definately the right size for the 2GM20.

Cheers
Andrew

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If the memories are better than the dreams then it's all over.....
[url=http://www.contessa26moonshine.me.uk]www.contessa26moonshine.me.uk[/url]

eebygumcaptain's Website

  • From: Victoria, BC
  • Registered: 2005-05-21
  • Posts: 47

Re: Hull Speed

Mark Sherlock's Website

  • From: Ile-Perrot, Quebec, Canada
  • Registered: 2005-09-11
  • Posts: 24

Re: Hull Speed

The 13 inches 3 blades is the std propeller for the 2GM20, but what is the pitch of the prop ?

Also there is not enough blade tip clearance, it should be at least 10% of prop diameter (1.3 inch). This could cause cavitations, vibrations and lost of performances. To be safe, the aperture design of the Contessa 26 doesn't allow more than a 11 inches diameter prop.

Michel F's Website

  • From: Belle River, Ontario
  • Registered: 2005-03-20
  • Posts: 143

Re: Hull Speed

8 Reply by stefan_d (edited by stefan_d 2006-03-20 19:25:53)

  • From: Ottawa, On
  • Registered: 2005-03-10
  • Posts: 353

Re: Hull Speed

If you can get about 3400 rpm out of the engine, then you've got the right prop.  When you wind her up, does it sound like you're driving your car around and you've upshifted too early?  Sans tach, thats about the only way to describe.  If you're underpitched, it'd be like driving around in first doing about 50 miles an hour.

If you're getting, or convinced you're getting, full revs out of your engine then maybe it's time calibrate your knotlog...  They're not known for being the most accurate of devices....

13" does seem big to me.....  The prop on mine was a 11x13" 3 blader, which to me seems overpitched, I'm probably going to replace with a two blade 12x9  or so.  Don't really know how she performed under power before, and don't really care.  If it was practical to cruise Lake Ontario without an engine, well, I'd have more room for beers.......

stefan_d's Website

  • MCo26
  • Veteran Member
  • Offline
  • Registered: 2005-04-24
  • Posts: 59

Re: Hull Speed

Andrew,

Your speed(4.4 knots) do you get it from the speed log or from the gps?

It's not the same at all. Gps give you speed above the ground and the speed log : speed on the water.  Let say you go north at 4 knots (from the speed log) and the flow of the tide is 2 knots (north again) then the gps will give you 6 knots.

Marc

Contessa 26 #158
Sun Wave
Montreal QC
  • From: Victoria, BC
  • Registered: 2005-05-21
  • Posts: 47

Re: Hull Speed

most likely there will not be 2 knots of current in your marina!!

Mark Sherlock's Website

  • From: Manchester, England
  • Registered: 2005-10-04
  • Posts: 59

Re: Hull Speed

Hi, thanks for all the feedback ... to answer a couple of questions. The speed was measured using a new NASA Clipper thru hull log, so it was the true speed as obviously no current in the locked in marina ! To answer Mark's point there is no black or white smoke from the exhaust, it's fairly clean so I don't think it's burning too much/too little fuel.

When the boat was out the water I measured the diameter of the prop and it was definately a 13", I'm not surprised that the Contessa was designed for an 11" or thereabouts as that would explain the very narrow gap !  I never measured the pitch at the time (how do I do that)

I'm tempted to get the marine engineer from the marina back in to give a quick check of the RPM and compression and see if he can spot anything else - which is going to be cheaper than hauling the boat out and back in again. Otherwise after I've put my 58Kg on new chain in the bow which has just arrived (40m 8mm short link) along with the inflatable and outboard which should flatten out the waterline, the only difference can be the prop ? I've dropped an email to one of the previous owners of the boat in the early 90's (who owns anothe Contessa now) to see if he can recall what he typically got out of the engine.

Cheers
Andrew

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If the memories are better than the dreams then it's all over.....
[url=http://www.contessa26moonshine.me.uk]www.contessa26moonshine.me.uk[/url]

eebygumcaptain's Website

  • From: Victoria, BC
  • Registered: 2005-05-21
  • Posts: 47

Re: Hull Speed

I think you might have just stated your proplem.  Your NEW speed log may need calibration,  when I first installed my new knot meter I was gettin readings over a knot below my actual speed.  Have a look into that before you start calling marine engineers because that sounds expensive!!

Mark Sherlock's Website

  • From: Vancouver, B.C. Canada
  • Registered: 2005-05-06
  • Posts: 304

Re: Hull Speed

Even with my boat loaded up with all the stuff I like to carry, (and you are talking to Miss Prepared for Anything here!) including chain in the bow and THREE anchors, ETC!! and my boat does 5.5 - 6.0k or so.
I have the Farymann with the slightly larger, NEW piston, head & cylinder, but still only about 8hp.   I have a 2 blade 12x9 RH Prop.
So I can go kinda fast?!

“You get a boat for only one reason, because you want one.  If you’re worried about being practical, forget boats.”
  • From: Manchester, England
  • Registered: 2005-10-04
  • Posts: 59

Re: Hull Speed

Mark,
That's a good idea about caliberating the log,  why did I not think of that !

I checked the manual and sure enough it can be caliberated but I never had time today to try some Contessa 26 drag racing up and down the marina ! I'll  let you know how I get on.

Cheers
Andrew

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If the memories are better than the dreams then it's all over.....
[url=http://www.contessa26moonshine.me.uk]www.contessa26moonshine.me.uk[/url]

eebygumcaptain's Website

  • From: Menai Strait
  • Registered: 2005-04-11
  • Posts: 12

Re: Hull Speed

  • From: Menai Strait
  • Registered: 2005-04-11
  • Posts: 12

Re: Hull Speed

17 Reply by eebygumcaptain (edited by eebygumcaptain 2006-03-31 14:01:38)

  • From: Manchester, England
  • Registered: 2005-10-04
  • Posts: 59

Re: Hull Speed

----------
If the memories are better than the dreams then it's all over.....
[url=http://www.contessa26moonshine.me.uk]www.contessa26moonshine.me.uk[/url]

eebygumcaptain's Website

  • From: Homer
  • Registered: 2005-11-01
  • Posts: 104

Re: Hull Speed

I ended up repitching my 12x9 two blade to match better with the newer Yanmar 1gm.  It works great...I get up toward 7 knots when full out, but I only get around 3200 rpm...hope that is ok...I usually cruise at about 25-2700 rpm.

  • From: Tucson AZ USA
  • Registered: 2005-06-03
  • Posts: 107

Re: Hull Speed

My 1GM10 with a 3 blade 11X10 prop gives me 5.5 Kts at 2800 Rpm.

Peter SC's Website