Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 27-08-2012, 13:58   #16
Senior Cruiser
 
SkiprJohn's Avatar

Cruisers Forum Supporter

Join Date: May 2006
Location: Kea'au, Big Island, Hawaii
Boat: Cascade, Sloop, 42 - "Casual"
Posts: 14,192
Re: Largest auxiliary engine possible

I once had a fisherman aquaintance who bought a sailboat and installed a V8 GM diesel and wondered why he couldn't motor more than 7-8 knots in his 40 foot displacement sailing vessel.
I think hull speed is an interesting concept that bears learning about early in a persons sailing career.
kind regards,
__________________

__________________
John
SkiprJohn is offline   Reply With Quote
Old 27-08-2012, 16:53   #17
Registered User
 
GreggL's Avatar

Join Date: Feb 2012
Location: NYC
Boat: Hunter E33
Posts: 194
Quote:
Originally Posted by skipmac

OK. So what is the max rpm rating for the engine?
Max is 3600 I believe
__________________

__________________
GreggL is offline   Reply With Quote
Old 27-08-2012, 17:30   #18
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,051
Re: Largest Auxiliary Engine Possible

Check the prop for size, pitch, position. Sometimes that can be tweaked as well.
__________________
hellosailor is offline   Reply With Quote
Old 27-08-2012, 19:53   #19
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,381
Re: Largest Auxiliary Engine Possible

Quote:
Originally Posted by GreggL View Post
Max is 3600 I believe
If the engine is rated at 3600 rpm, confirm by revving it to 3600 rpm in neutral, and you can only get max 2600 rpm under power then I think you are seriously overpropped.

You should be able to reach close to the rated max rpm under power. If the diameter of the prop is right then you should look into reducing the pitch.
__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 27-08-2012, 21:13   #20
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,455
Re: Largest Auxiliary Engine Possible

Quote:
Originally Posted by skipmac View Post
If the engine is rated at 3600 rpm, confirm by revving it to 3600 rpm in neutral, and you can only get max 2600 rpm under power then I think you are seriously overpropped.

You should be able to reach close to the rated max rpm under power. If the diameter of the prop is right then you should look into reducing the pitch.
This is all correct... if the hull and the prop are free of fouling. An astonishingly small (to the untrained eye) amount of fouling can cause symptoms that are very similar to overpropping. Better have a good look underwater before committing much money to modifications.

Cheers,

Jim
__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is online now   Reply With Quote
Old 27-08-2012, 22:05   #21
Registered User

Join Date: Nov 2011
Location: Montegut LA.
Boat: Now we need to get her to Louisiana !! she's ours
Posts: 3,421
Re: Largest Auxiliary Engine Possible

Ya might ck the throttle setting ! It could be not adjusted to open all the way !! Sometimes we forget to ck the simple stuff !! just my 2 cents cus 2600 on a motor rated for 3600 is goofey!LOL
__________________
Bob and Connie
bobconnie is offline   Reply With Quote
Old 27-08-2012, 22:08   #22
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,381
Re: Largest Auxiliary Engine Possible

Quote:
Originally Posted by bobconnie View Post
Ya might ck the throttle setting ! It could be not adjusted to open all the way !! Sometimes we forget to ck the simple stuff !! just my 2 cents cus 2600 on a motor rated for 3600 is goofey!LOL
Could be the problem which is one more reason why he should try revs in neutral.
__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 27-08-2012, 22:11   #23
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,381
Re: Largest Auxiliary Engine Possible

Quote:
Originally Posted by Jim Cate View Post
This is all correct... if the hull and the prop are free of fouling. An astonishingly small (to the untrained eye) amount of fouling can cause symptoms that are very similar to overpropping. Better have a good look underwater before committing much money to modifications.

Cheers,

Jim
Very good point. I think I was subconsciously ignoring that possibility since he seems to be reaching a good speed through the water at a reasonable rpm but fouling should be checked.

Maybe another question, did the engine ever reach rated rpm under load?
__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 28-08-2012, 00:52   #24
Registered User
 
jeremiason's Avatar

Join Date: Oct 2010
Location: Punta Gorda, Florida
Boat: Sea Ray 270
Posts: 1,427
Images: 2
Send a message via ICQ to jeremiason Send a message via Yahoo to jeremiason Send a message via Skype™ to jeremiason
Re: Largest Auxiliary Engine Possible

I did a quick internet search and your sister ships report making 7.3 knots, which I assume was full throttle. Just search the internet for "hull speed hunter 33" and you will find two other threads about this on other sail sites.

If you follow the previous suggestion and find the engine will make 3600 rpms in neutral, then the prop is probably over pitched... Did the previous owner change props?
__________________
Tom Jeremiason
Punta Gorda, Florida

jeremiason is offline   Reply With Quote
Old 28-08-2012, 01:34   #25
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Largest Auxiliary Engine Possible

couple of reasons why you might want a more powerful engine - crossing bars, towing other boats. 29hp on a 33 ft boat sounds pretty good to me, my 38 ft lump gets hull speed from a (very old) 20hp.
__________________
charliehows is offline   Reply With Quote
Old 28-08-2012, 05:36   #26
Registered User
 
GreggL's Avatar

Join Date: Feb 2012
Location: NYC
Boat: Hunter E33
Posts: 194
Speaking to engine and throttle. This was a new boat with new motor. Hs it ever reved at 3600 rpm, no. But ive gotten it to almost 3000 under load. Yanmar just did a 50 hour service and gave me the green light. Since then I can't get past 2600 really, but am attaining the same speed.
__________________
GreggL is offline   Reply With Quote
Old 28-08-2012, 06:07   #27
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,381
Re: Largest Auxiliary Engine Possible

Quote:
Originally Posted by GreggL View Post
Speaking to engine and throttle. This was a new boat with new motor. Hs it ever reved at 3600 rpm, no. But ive gotten it to almost 3000 under load. Yanmar just did a 50 hour service and gave me the green light. Since then I can't get past 2600 really, but am attaining the same speed.
Assuming a few things like a clean prop and bottom, no problems with transmission, no crab pot lines wrapped around the shaft, etc your max of 2600 rpm sounds much too low.

Some approximate numbers, the engine rpm should be around 3000 at cruising speed, say 6-6.5 kts. and you should be able to reach at least 3400 rpm at max throttle. This would be in calm wind and wave conditions.

If the prop is to big for the engine you are overloading the engine and risking long term problems. Think of driving a car up a steep hill at low speed in high gear.

Another question, youi say the max rpms dropped after servicing the engine? Are you sure the tach is correct?
__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 28-08-2012, 06:58   #28
Registered User
 
GreggL's Avatar

Join Date: Feb 2012
Location: NYC
Boat: Hunter E33
Posts: 194
Quote:
Originally Posted by skipmac

Assuming a few things like a clean prop and bottom, no problems with transmission, no crab pot lines wrapped around the shaft, etc your max of 2600 rpm sounds much too low.

Some approximate numbers, the engine rpm should be around 3000 at cruising speed, say 6-6.5 kts. and you should be able to reach at least 3400 rpm at max throttle. This would be in calm wind and wave conditions.

If the prop is to big for the engine you are overloading the engine and risking long term problems. Think of driving a car up a steep hill at low speed in high gear.

Another question, youi say the max rpms dropped after servicing the engine? Are you sure the tach is correct?
I guess this brings us to another issue all together. Didn't even realize that I'd had much of a problem.

How can I tell is my tach is wrong?
__________________
GreggL is offline   Reply With Quote
Old 28-08-2012, 10:15   #29
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,381
Re: Largest Auxiliary Engine Possible

Quote:
Originally Posted by GreggL View Post
I guess this brings us to another issue all together. Didn't even realize that I'd had much of a problem.

How can I tell is my tach is wrong?
My best suggestion, if you can rev the engine in neutral and see +/- 3600 rpm on the tach but cannot get over 2600 in gear then I would think the tach would be OK. An engine expert might offer some comments here.

Have you inspected the prop or when was the last time you hauled and cleaned? Can you snorkel down to take a look to confirm the prop has no fouling at all?

Also, do you feel any vibration coming from the drive train when motoring at full throttle?
__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 28-08-2012, 10:20   #30
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,381
Re: Largest Auxiliary Engine Possible

By the way, it's not like your engine is going to explode or melt down into a puddle of scrap metal the next time you go cruising. Just from my somewhat limited and untrained understanding it is not good for the long term health of a diesel engine to constantly run it overloaded (to much prop so running at too low rpm) or idling (like for charging batteries) and underloaded.

The principle here is that internal combustion engines develop their max power at a certain rpm. Running at a much lower rpm under load puts more strain on the engine.
__________________

__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Reply

Tags
engine

Thread Tools
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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 12:38.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.