Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 19-09-2020, 23:46   #1
Registered User

Join Date: Oct 2017
Location: Sunshine Coast, QLD
Boat: Roberts 370 Expedition
Posts: 36
Engine Rev accuracy

Hi All. I am about to take ownership of an aluminium yacht which has a 50hp Perkins Prima deisel. She has a s/s Autostream S1 self-feathering prop with adjustable pitch. Based on the rev counter, the pitch has been set for the engines Maximum Rated Speed of 3,000rpm.

The thing I have noticed is that at 3,000rpm (per the guage), the yacht speed through the water is only 5knts. Her displacement is only 8.9 tons and I would have expected a higher speed for this "weight". The prop cavitates at revs higher than 3,000rpm so effectively there is no useable power left.

At the wharf, the engine revs to 5,000rpm wide open throttle and not under load.

I don't know if such high revs (5,000rpm) are normal and am wondering if the rev counter is reading far too high engine revs. My aim is to make sure the prop is adjusted properly for the engines Max Rated Speed of 3,000rpm. But I don't know if the gauges are reading rpm correctly.

Any constructive suggestions appreciated.
Wideocean7 is offline   Reply With Quote
Old 20-09-2020, 00:02   #2
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 11,686
Re: Engine Rev accuracy

You could get a hand held tachometer and check it for yourself. This is sample but there are dozens of others on eBay etc.

https://www.jaycar.com.au/digital-tachometer/p/QM1448
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is online now   Reply With Quote
Old 20-09-2020, 11:44   #3
Registered User

Join Date: Mar 2006
Location: Nevada City. CA
Boat: Sceptre 41
Posts: 3,838
Images: 9
Re: Engine Rev accuracy

Just went through this exercise with my Yanmar to get fit for a new prop. I think it is important to get both the speed at the crankshaft and after the reduction gear. I used a harbor freight tool worked fine.
__________________
Fair Winds,

Charlie

Between us there was, as I have already said somewhere, the bond of the sea. Besides holding our hearts together through long periods of separation, it had the effect of making us tolerant of each other's yarns -- and even convictions. Heart of Darkness
Joseph Conrad
Charlie is offline   Reply With Quote
Old 20-09-2020, 21:55   #4
Registered User
 
Fore and Aft's Avatar

Join Date: Jan 2015
Location: Gympie
Boat: Volkscruiser
Posts: 1,343
Re: Engine Rev accuracy

Wideocean7 according to the brochure 3000 rpm is where your Perkins max rpm should be at. That link below has a manual you can download.
I see the Perkins M80T has the 4500 RPM? I googled some images of one and compared my survey photos and boy they look similar.
I also found an exploded diagram of your prop. Those two nuts on the left of the Prop assembly are going to become your new best friends. I really cannot see any way you can properly/cheaply adjust the prop without diving on it and adjusting those bolts. The other way is going to be adjusting the prop, get dropped in the water, sea trial then back to the travel lift to get lifted and repeat the process. I know it took about three swims before I was happy with my prop pitch.
Cheers
https://www.martec-props.com/install_Autostream.htm
https://forums.sailboatowners.com/th...22.1249923404/
Fore and Aft is offline   Reply With Quote
Old 20-09-2020, 22:50   #5
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 4,160
Images: 7
Re: Engine Rev accuracy

If the rev counter is taking it's signal from the output on the alternator the reading can be affected by a number of factors ither than true engine speed. Belt slippage for instance.
RaymondR is offline   Reply With Quote
Old 21-09-2020, 01:19   #6
Registered User

Join Date: Oct 2017
Location: Sunshine Coast, QLD
Boat: Roberts 370 Expedition
Posts: 36
Re: Engine Rev accuracy

Thanks all. Your comments are appreciated. It sounds as if first, I need to check the revs to see if the gauge is reading correctly and second adjust the prop accordingly. Does anyone have any instructions how to measure crankshaft/prop shaft revs if I buy a tachometer? (Yep, I have Googled it!). Fore and Aft - I will be in the water multiple times amongst the dolphins and sharks.

Thanks again. Andy
Wideocean7 is offline   Reply With Quote
Old 21-09-2020, 01:31   #7
Registered User

Join Date: Nov 2013
Location: Nice, France
Boat: Hunter Marine 38
Posts: 967
Re: Engine Rev accuracy

Just glue a piece of the refective tape on the crankshaft and point the laserdot of the rpm gun on it. Easy.
sailormed is offline   Reply With Quote
Old 21-09-2020, 03:31   #8
Registered User
 
Fore and Aft's Avatar

Join Date: Jan 2015
Location: Gympie
Boat: Volkscruiser
Posts: 1,343
Re: Engine Rev accuracy

Andy it will be interesting to see if the gauge is wrong. When do you take possession of your yacht?
Cheers
Fore and Aft is offline   Reply With Quote
Old 21-09-2020, 04:19   #9
Registered User

Join Date: Oct 2017
Location: Sunshine Coast, QLD
Boat: Roberts 370 Expedition
Posts: 36
Re: Engine Rev accuracy

5hrs ago😀!!
Wideocean7 is offline   Reply With Quote
Old 21-09-2020, 04:28   #10
Marine Service Provider
 
Snore's Avatar

Join Date: Jan 2011
Location: St. Petersburg, FL
Boat: Tartan 33 and OPB
Posts: 2,883
Send a message via Skype™ to Snore
Re: Engine Rev accuracy

There is an app for that! Check App Store, I found one for my iPhone that uses the phone’s flash as a strobe tachometer. Cost was under $3USD
__________________
"Whenever...it requires a strong moral principle to prevent me from deliberately stepping into the street, and methodically knocking people's hats off- then, I account it high time to get to sea..." Ismael -a link to my delivery website is in my profileó
Snore is offline   Reply With Quote
Reply

Tags
engine

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Accuracy of Passage Weather ? Sabbatical II Seamanship & Boat Handling 7 11-01-2012 16:30
iPad vs Garmin - Accuracy ? Username33 Marine Electronics 3 13-08-2011 18:32
Acceptable Accuracy in Celestial Navigation sneuman Navigation 43 02-02-2011 19:45
Engine Won't Rev in Gear n8cal@hotmail.c Engines and Propulsion Systems 15 16-06-2009 09:44
Astronav. Instrument accuracy and other meanderings. skookum Navigation 13 15-03-2009 10:03

Advertise Here


All times are GMT -7. The time now is 23:33.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.