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2005 SIgnature 260 Signature cruising speed

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I have been researching expecting cruise speed/rpm/GPH numbers of chaparral 260 Signatures of my vintage and I don't know if the numbers I am getting are normal.  I have a Volvo Penta 5.7 GI and volvo duo prop.  The engine is brand new from 2019 and has about 23 hours on it.

 

Last time out, 1 ft waves in Boston harbor, 10knt wind across the bow from port to starboard. 

3400 RPM - Barely on plane
3600 RPM - 18kts
3800 RPM - 20kts
4000 RPM - 21-22Kts

The boat has fresh bottom paint but it does look like it could have been sanded better before painting (purchased it 2 months ago). From other threads I have seen and from other research, I would expect to see a few more kts/hr with my boat/engine/drive combo?  NOTE: These numbers were taking with 1/2 tank fuel, 1/2 tank water and 4 adult men on board.

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For reference, I have a 2004 260 Signature with 5.7 Gi duoprop, and at 3800 rpm it cruises around 34 mph  (30 kts).

It goes on plane around 25 mph.

 

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Do you know how to trim the drive for best speed ?

Does the boat have ACCURATE working hull TRIM TABS ?

Are you using GPS speed ?

Are you sure your tachometer is accurate ?

 Is the bottom of the hull full of water? 

Is the correct propeller on the boat. 

 Is there junk wrapped around the prop ?

How many people were in the boat to get your numbers ?

 

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11 hours ago, cyclops2 said:

Do you know how to trim the drive for best speed ?
Yes I trim the boat property. I trim up and watch for RPMs to rise until I hear the prop ventilate, then I drop it down a few clicks.

Does the boat have ACCURATE working hull TRIM TABS ?

The trim tabs are operational and I do believe they are retracted all the way.

Are you using GPS speed ?

Yes I am using gps speed on my Garmin gps

Are you sure your tachometer is accurate ?

I do believe it is accurate because it hovers at 20mph when the gps is also reporting 20mph

 Is the bottom of the hull full of water? 
Yes there is a little bit of water that is not completely sucked up by the bilge pump

Is the correct propeller on the boat. 
The engine and our drive were professionally replaced last year. I assume the correct prop was installed. I don’t actually know what props are installed 

 Is there junk wrapped around the prop?

i checked the prop before the last time out, it was clear of debris and growth

How many people were in the boat to get your numbers ?

there were four adult males with full 40 gallons of water and 1/2 tank (40 gallons) of fuel

 

All great questions. I’ve answered them in bold in then body of your response.

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Can you squirm under the dash & see the back of the tachometer ?  See if it has a small moveable lever to select different engine with different number of cylinders . That RPM rate is just about 2 x what it should be.  Get lucky  :D

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2 minutes ago, cyclops2 said:

Can you squirm under the dash & see the back of the tachometer ?  See if it has a small moveable lever to select different engine with different number of cylinders . That RPM rate is just about 2 x what it should be.  Get lucky  :D

lol are you serious?

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About the props. YOU MUST VERIFY what is on the drive. Super important that they did not get changed some how.  If we believe the rpms to boat speeds ? You have the most useless prop in the world.

I am serious if your tach has a selector on the back of it.  Set it to 8 if it is selectable.

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Look at the RPM to water speeds of the other 2 boaters.

I usually am concerned when the 10 X water speed does not come close to the RPMS.

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1 hour ago, cyclops2 said:

My error for not seeing your speed in Knots.   Need to do a conversion on the web.

No problem at all.  I'm just trying to get a feel for if something is wrong or not.  Out in the harbor there is awlays some chop and usually a 10 mph wind or so. I know chop will slow me down, but even in sub 1ft waves, I have never seen over 25kts on the GPS at WOT which if I recall correctly was about 4700 RPM.

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2 hours ago, cyclops2 said:

Can you squirm under the dash & see the back of the tachometer ?  See if it has a small moveable lever to select different engine with different number of cylinders . That RPM rate is just about 2 x what it should be.  Get lucky  :D

The more I think about this, I don't think there would have been any reason for this to have been switched by mistake when they re-powered. The tac still shows the original engine hours (all gauges are original)

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In a marine shop ?  There could have been more than just your drive off and leaning against the wall. Somebody has a Lugging boat & engine that can not plane at all.

Stuff like that does happen.  

Have some one connect a tachometer to your engine to get ACCURATE rpms at different speeds.  If you are accurate ? you have the wrong prop  /  drive on the boat.

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1 hour ago, cyclops2 said:

In a marine shop ?  There could have been more than just your drive off and leaning against the wall. Somebody has a Lugging boat & engine that can not plane at all.

Stuff like that does happen.  

Have some one connect a tachometer to your engine to get ACCURATE rpms at different speeds.  If you are accurate ? you have the wrong prop  /  drive on the boat.

 

OK, The next time I am at the boat I will check. I hope I am able to get a close enough look with the drive trimmed all the way out. With that said, what prop set SHOULD it have? I just looked back through the receipt of all of the work done and I did see that they "rehubbed the props"?

 

Also, is there any chance that a really rough bottom could be causing the disparity? 

 

One more piece of data:  I just dug through the sea trial report from my surveyor:

"Manufacturer's recommended max RPM is 5000 - Engine reached 4700 RPM and a
speed of 30 Knots at full throttle while under load. Considering these readings the
engine is operating normally."

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I just dug through the receipts of the repower/re-drive and it turns out that the new outdrive is the following:

Volvo Penta Dps-B Drive Unit 1.95:1 Ratio (Part Number VOLVO-21766684)

Does anyone know if this is the original ratio out drive that came with the boat? A change in ratio with the same prop set could also effectively change the final prop ratio.

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I thought most were 1.78 ratio but I could be wrong. The real key here is, are you making rated WOT rpm?  If 5000 is rated and you’re getting 4700, you’re not too far off.  The problem with VP Duoprops is that the props are so expensive it is costly to experiment. But I for sure think you should get better than 30kts at WOT on that boat.  I had a runabout that was overpropped, it had a 21 on it. I put a 19 on it and it totally changed the boat, it freed that motor up big time. 

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I agree something is wrong here.  My 264 with a 6.2L Merc gets 25 knots at a 3500 rpm cruise and 40 knots at wot.  FWIW, I bought it with a badly peeling bottom paint job which has all been blasted off and replaced with some super slick VC17.  I might of picked up a knot or two by getting that redone, nothing dramatic.

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8 hours ago, cyclops2 said:

When they re- hubbed the props .  Did you get the right ones put back on ?  

The work was done by the previous owner, I have no idea what happened. I also tried to trim the drive all the way up today before I went out but I could not identify the props.

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Make a New thread. Asking what props sholud be on that gear ratio drive unit.  Or even the other gear ratio drive...  Might get very lucky from others with similar motor & drives.

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