Reply
 
Thread Tools Display Modes
 
Old 09-12-2011, 08:55 PM   #1
Member
 
mc14's Avatar
 
Join Date: Sep 2011
Posts: 7
Normal Engine RPM's

I own a 1974 Willard Vega with a 50HP Perkins. The Perkins has about 3400 hours on it. After reading the owners manual, and the Perkins Engine Manual, I still can't find out what the normal RPM's should be while underway. I currently run between 2000 and 2300. Can anyone comment on that?
__________________
Advertisement

mc14 is offline   Reply With Quote
Old 09-12-2011, 09:20 PM   #2
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,711
RE: Normal Engine RPM's

Sure I can comment on that. I had a Perkins 4-107 before re-powering w a 4-107 Mitsubishi. Your Perkins is rated for 36hp at 3000rpm, 42hp at 3600rpm, and 50hp at 4000rpm. I don't know how the other ratings figure in on it but the 36hp rating is the one you need to consider. It's been awhile w the numbers so check on the 36hp but 3000rpm is where you need to be. Run the engine at wide open throttle (WOT) under normal conditions. You should turn up to 3000rpm. If not you need to re-pitch the prop to attain 3000rpm. Then you can run 1800 to 2500rpm while cruising and not overload your engine. Willard over pitched the W30s one inch so top rpm was 2750 approx so it's very likely that's what your boat will do. And at 2750rpm your Perkins is only putting out about 33hp. That part is OK as it only takes about 18hp to cruise a bit over 6 knots. Hull speed is achieved at 7 knots and after you get your prop pitched correctly you should be able to achieve about 7 knots. By the way there's no "rpms", it's always rpm. I'd love to see some pics of your Willard in the* the photo gallery at the top of general discussion. Welcome to the forum and please participate with us. Also notice the Willard section near the bottom of the thread list. I'm anxious to see your boat Mike.
__________________

Nomad Willy is offline   Reply With Quote
Old 09-12-2011, 09:40 PM   #3
Guru
 
kolive's Avatar
 
City: Vashon Island, WA
Country: USA
Vessel Name: Island Breeze
Vessel Model: 1974 Grand Banks 36-427
Join Date: Sep 2011
Posts: 582
Send a message via Skype™ to kolive
RE: Normal Engine RPM's

Hello,

*

I own a 77 Willard with a Perkins 4-108 and we run it at 2000 rpm.* I have not run it at 3000 or above like Eric discusses so I have no experience at that rpm.* We cruise right at 6 knots with 2000 rpm.

Keith Olive
kolive is offline   Reply With Quote
Old 09-12-2011, 09:49 PM   #4
Member
 
mc14's Avatar
 
Join Date: Sep 2011
Posts: 7
RE: Normal Engine RPM's

Thanks for the skinny Eric, that is exactly what I was looking for. In fact, that's what seemed to be the sweet spot for the engine and what I have been running at. I will have the prop adjusted on my next pull. I have only owned her for a few months and it seems like she has been in the shop for most of that time. She is back with me now and I hope to have some pic's done and loaded within the next two weeks. Thanks again for the help and I look forward to participating in the forum.
mc14 is offline   Reply With Quote
Old 09-12-2011, 09:57 PM   #5
Member
 
mc14's Avatar
 
Join Date: Sep 2011
Posts: 7
RE: Normal Engine RPM's

Thanks Keith, that's where I have been running and the way I understand Eric, that's just about perfect. I only need to run her up to 3000 to check the pitch of my prop. Running at 3000 is wide open and you don't want to do that for long.

What type of oil pressure do you have, I have been running around 65 lbs which seems a bit high. Thanks again for the help.

Mike Connor
mc14 is offline   Reply With Quote
Old 09-13-2011, 04:29 AM   #6
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
RE: Normal Engine RPM's

"18hp to cruise a bit over 6 knots."

18 hp should easily be had at 1600 to 1800. Look at the mfg HP graph.

Many folks would intentionally over size the prop (aka cruising prop) to bring the normal cruise down to quieter levels.

Just be sure , where ever you set the cruise rpm you can obtain 300rpm higher with the throttle.

In other words run WOT , note the rpm obtained and drop 300rpm or more to cruise.
FF is offline   Reply With Quote
Old 09-13-2011, 06:51 AM   #7
Guru
 
kolive's Avatar
 
City: Vashon Island, WA
Country: USA
Vessel Name: Island Breeze
Vessel Model: 1974 Grand Banks 36-427
Join Date: Sep 2011
Posts: 582
Send a message via Skype™ to kolive
RE: Normal Engine RPM's

Mike,

My oil pressure has been around 50 and my temp is 145, running at 2000 rpm.* Ran this way to Desolation Sound and Princess Louisa this summer.*

*

Keith
kolive is offline   Reply With Quote
Old 09-13-2011, 09:01 AM   #8
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,711
RE: Normal Engine RPM's

Kolive and mc 14,

Fred has this thing in his head that says a boat should be overpropped so if you buy into this or have any doubts about how to properly prop and load your engine talk to reputable propeller shops, read manuals and talk to engine distributors, manufacturers and OTHER people on this forum. Don't talk to one. Talk to as many as you have time for as opinions occasionally vary especially from mechanics. Engineers are best.
Nomad Willy is offline   Reply With Quote
Old 09-13-2011, 09:19 AM   #9
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
RE: Normal Engine RPM's

"Fred has this thing in his head that says a boat should be overpropped"

Not really , I think any boat with an oversized engine should be operated in its optimum range.

This boats engine is 100% oversized ,at 36 hp, really silly at 50hp , and only needs 18 hp but the mfg recommends a prop to absorb 36hp at WOT.

Since the boat will almost never be operated at WOT , the service life running at a more rational RPM is an easy way to extend engine life 2x or perhaps more.Fuel burn will be lower too.

The mfg recommends a WOT prop as some folks will actually cruise there.

If you ever wondered why the bare boat charter buckets in the Carib seldom see 1/5 of the engine service life a normal cruiser would , its from WOT from start to shutdown.

The mfg LOVE a cruiser with a WOT prop as at normal cruise RPM only a fraction (about 1/2- 1/3 ) the rated power at that RPM is being used.
This helps guarentee hassles on a new engine.
Any problems from underloading show up years later , off his tab , but on yours.

The poorer fuel burn is also not his problem.
FF is offline   Reply With Quote
Old 09-13-2011, 10:16 AM   #10
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,711
RE: Normal Engine RPM's

If I was to over prop my engine (rated at 3000) to WOT at 2700rpm it is very obvious the engine will be overloaded at WOT. What about 2500rpm? 2300? 2400? Who knows at what rpm the engine will be overloaded and at what rpm it will be safe to operate. If it's getting dark and you want to get to an anchorage before dark and it's questionable if you'll make it you'll want to push the boat but you can only guess where the operational red line is and if you DO push it there's a good chance the engine would be overloaded and some engine parts could get damaged. If your'e propped correctly by the engine manufacturer's specifications you can get the most out of your engine and your boat and know your engine will not be damaged from overloading. But if fuel consumption is all you care about you can save a small amount by overpropping as Fred suggests.
Nomad Willy is offline   Reply With Quote
Old 09-13-2011, 04:56 PM   #11
Member
 
mc14's Avatar
 
Join Date: Sep 2011
Posts: 7
RE: Normal Engine RPM's

I really appreciate the info on the proper size prop, makes sense to me. I will run her WOT the next time I'm out and post what I find. Then have the prop adjusted at my next pull. I'm really glad I found the forum and look forward to future visits.*I
mc14 is offline   Reply With Quote
Old 09-14-2011, 04:06 AM   #12
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
RE: Normal Engine RPM's

"you'll want to push the boat but you can only guess where the operational red line"

For almost all setups 10% less rpm than WOT is a good red line.

I recommend 300rpm reduction to be even further down the power slope.

The question then is the boats operator skilled , and willing to operate the boat as set up.

Or Brain Dead and in need of a WOT forever prop and always accept the problems noise ,and service life that choice requires

DO it Your Way!
FF is offline   Reply With Quote
Old 09-14-2011, 12:39 PM   #13
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
RE: Normal Engine RPM's

Quote:
DavidM wrote:You are asking it to do something it was never designed to do, putting out peak torque at less than wot rpm.

And don't ever think about overpropping a modern, tubocharged, high output diesel. These are marginal enough at normal propping. Overprop and the exhaust gas temperature shoots up. That and the extra torque related mechanical stresses will kill them before their prime.
At great risk of starting something resembling the single vs twins debate, I have to make a couple of comments.

Unless you mean maximum torque, "peak torque"*is a moving target and is simply the highest torque obtained under a given condition. Maximum torque is always*produced well below WOT - whatever that means because a diesel engine doesn't have a throttle, it has a speed setting and a maximum fuel setting. If the engine reaches maximum speed the governor reduces fuel to maintain that speed. If it reaches maximum fuel flow, the governor reduces fuel*at that point. The lever on the*governor merely sets the balance point of a set of flyballs or an electronic null point, it doesn't do anything else.

A fixed pitch propeller's free running*torque demand is roughly the square of the rpm, as rpm increases, the torque required to spin it increases proportionally. That is why there is a difference between a propeller curve and an engine power curve.

An old mechanically governed NA diesel can easily be overloaded by "over propping"*or even*leaning a bit heavily on the power lever, or a sudden increase in current on the bow or even a sharp turn with a twin. The governor will deliver all the fuel it can up to the fuel stop in an attempt to reach the speed setting. The engine will smoke like crazy and will almost certainly run high exhaust temperatures. Even propped correctly this is often an issue because fuel is delivered more quickly than the engine can accelerate. In this case the overpropped powertrain won't necessarily wear due to higher mechanical stresses, it will suffer from high thermal stresses*and destroy the top end first.

The case described is very similar to tugboats or ice breakers*with engines that*are capable of producing far more torque than required for free running. They have a pair of propeller curves, free running in open water at full speed, and a second curve that reflects the much earlier rise (same torque but at a lower speed) that occurs when the boat speed is low due to heavy towing or restrained by ice or the prop turning in dense slush. They use a torque limiting governor that kicks in to*reduce fuel to limit torque to a predetermined relationship to rpm.

And this brings us up to the modern high strung turbocharged stallions that drive some*of the newest*boats. Because they are so well monitored by the engine control system the chance of overloading them due to a heavy hand on the power lever or overpropping is even less likely. The turbochargers are fitted with wastegates, the governor receives a signal from the inlet manifold so it knows how much air is available and if it is or is not within limits for the rpm or fuel flow that exist at that moment.

My take on this discussion is that, sure, you can overprop so as to bring the engine power curve more inline with the propeller torque curve but that will occur at a much lower horsepower output with a fixed pitch propeller so you will limit your top speed and power reserves. You will lose a broad band of speed and power options and increase the negative impact of headseas and winds. You will have to (or should)*reset your governor fuel stops and learn how to "ramp up" engine power like the big ships do.

As far as mechanical wear is concerned, a slower turning engine is far less prone to wear than a faster turning engine. The increased cylinder pressure and loads are easily handled by the bearings of an industrial or marine engine. I would concentrate on limiting thermal loads.
RickB is offline   Reply With Quote
Old 09-14-2011, 06:38 PM   #14
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,711
RE: Normal Engine RPM's

David and Rick,

Very good posts both and little to argue w or call wrong. FF, I think one would need to go down more than 10% to get to an engine speed that could be considered continuous or free of over loading on an over propped system. Five percent on a properly propped system (100rpm approx) but with an over propped boat (FL 300rpm over propped) you'd need to go down another 300 to get to safe territory but it's any man's guess. This means you could'nt come even close to 2000rpm (in excess of 500rpm below rated) before hitting never never land. FF says "For almost all setups 10% less rpm than WOT is a good red line.I recommend 300rpm reduction to be even further down the power slope." Sounds for sure you are a bit vague about where the cliff or the brick wall is FF. Exactly my point. The average boater would'nt know how to operate the boat without damage. So if one over props a boat it should be propped correctly before he sells it. Rick I think you achieved a great balance of deep tech and lay speak. Fully understandable. And enough information to not need to say where's the beef? Two things that come to mind on an over propped engine is that lube oil and coolant flow would be less but forces on many parts would be (it would seem) higher. I suspect though that due to the thermostat and the oil pressure relief valve that both fluids should be able to do their jobs as well as under normal loading. One set of parts in particular should wear much faster on the slower turning engine putting out the same power is the piston, cylinder and rings. There would be much more side loading on the piston and more pressure on the rings* ...especially keystone types. Pardon me for disagreeing w you Rick but I do think putting out the same amount of power at a lower engine speed will result in more wear at least with these parts. But I'll say this: If you had a 32 GB w 120 FL over propped 200rpm and could actually determine the rpm point where over loading starts and always operated it below that point it would be better than operating it propped normally by the book. One more comment I hang heavily on this post is that I doubt that any manufacturer would support over propping. Turbo, NA or whatever.
Nomad Willy is offline   Reply With Quote
Old 09-14-2011, 08:29 PM   #15
Guru
 
bobofthenorth's Avatar
 
City: Cowichan Bay, BC
Country: Canada
Vessel Name: Gray Hawk
Vessel Model: Defever 43 Offshore Cruiser
Join Date: Oct 2009
Posts: 570
RE: Normal Engine RPM's

For my money this is pretty much a tempest in a teapot but if one was particularly worried about overheating from being overpropped an EGT gauge would answer the question at a pretty nominal cost.*
bobofthenorth is offline   Reply With Quote
Old 09-14-2011, 09:34 PM   #16
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,711
RE: Normal Engine RPM's

Hi Bob,

The EGT tells the exhaust gas temperature (if installed right) so we know how much heat is in the exhaust pipe. Can one make assumptions about what the temperature of critical engine parts are inside the engine? Say my exhaust valves are 1000 degrees when my EGT says X is the temp of my exhaust gas. Then I take the EGT off that engine and install it on another engine and run it at X EGT. Are my exhaust valves on the 2nd engine at 1000, 700 or 1200 degrees. A good temp for one engine may not be good for another. I don't know but perhaps you, Rick or David does.

*
Nomad Willy is offline   Reply With Quote
Old 09-14-2011, 10:22 PM   #17
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,363
RE: Normal Engine RPM's

It is quite plausible to have low EGTs and still overheat the engine coolant gauge*- such as would occur with plugged strainers, BO raw water pump, gummed up HX etc.
sunchaser is offline   Reply With Quote
Old 09-15-2011, 04:33 AM   #18
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
RE: Normal Engine RPM's

"The average boater wouldnt know how to operate the boat without damage."

We are talking about a cruiser , not the usual 100 hour dock queen champ , with a Greek captains hat.

The EGT gauge , and perhaps some nail polish pips on the tach would be a fine reminder , when the boat is loaned..

EGT is fine for adjusting long or short term power settings ,marine/industrial mfg have the limits published .

Also forgotten in this discussion is the wide (sometimes 2-1 ) difference in cont power and pleasure boat power.

A marine engine mfg will usually show 4 ratings , my preference is to use the 24/7 power output to set the long range cruise power.

A panic WOT run to the dock may fall into the 400hours a year use area , and be no problem at all.

All part of the art of maximizing the engine to the intended use.
FF is offline   Reply With Quote
Old 09-15-2011, 08:34 AM   #19
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,711
RE: Normal Engine RPM's

Lets get back to basics here Fred. Why do you do this? I assume you overprop as you talk it up so much. What's the point? Why do it?
Nomad Willy is offline   Reply With Quote
Old 09-15-2011, 09:26 AM   #20
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 5,420
RE: Normal Engine RPM's

Quote:
nomadwilly wrote:
Lets get back to basics here Fred. Why do you do this? I assume you overprop as you talk it up so much. What's the point? Why do it?
* * * ** I have the same question.
__________________

Codger2 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

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
3208 T, Engine RPM jlamb15 Power Systems 8 10-20-2015 10:37 AM
Is this normal(battery charger fan)? Baker Electrical and Electronics & Navigation 12 06-11-2011 03:43 AM
High RPM = Hot Engine Dixie Life Power Systems 36 03-15-2011 04:49 PM
HP vs. RPM vs. Economy timjet General Discussion 22 01-07-2010 10:45 AM
8D Outgassing; how much is normal? Max Simmons Electrical and Electronics & Navigation 11 05-07-2009 01:06 PM




All times are GMT -5. The time now is 01:37 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012