Nomad Willy
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Mark is there a 50hp engine in that box astern?
Higher HP diesel?
- Thread starter Wanderin Star
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If you have answers, please help by responding to the unanswered posts.
markpierce
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Those aren't "trawlers" (capable of exceeding hull speed) in the Chapman sense. They're fast cruisers.
markpierce
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I'm clueless. How does the typical Turkish fisherman equip his boat? And I'm not certain what his secondary engine is: the oars or a possible engine.
FF
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"They do provide a prop demand fuel
curve but I haven't figured how to convert that to an efficiency curve."
That is because you cant.
ONLY a BMEP or fuel map will allow one to chose and match efficient engine speeds with desired rational cruise speeds.
curve but I haven't figured how to convert that to an efficiency curve."
That is because you cant.
ONLY a BMEP or fuel map will allow one to chose and match efficient engine speeds with desired rational cruise speeds.
go-planing
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The prop charts for our engines show prop demand fuel burn and power required at each rpm. With a hull speed versus rpm chart (owner generated) one can then get a pretty good idea of what's going on in terms of efficiency for that hull/engine combination. Guess you could substitute prop chart data for other engines to get a ball park comparison.
FF
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"With a hull speed versus rpm chart (owner generated) one can then get a pretty good idea of what's going on in terms of efficiency for that hull/engine combination.
Not really , it is fine (if its accurate ) to know what the burn might be at some chosen loading, but weather the the egine is at high or low efficiency (fewest GPH/HP is unknowable. ON PURPOSE.
Not really , it is fine (if its accurate ) to know what the burn might be at some chosen loading, but weather the the egine is at high or low efficiency (fewest GPH/HP is unknowable. ON PURPOSE.
go-planing
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Depends what you're trying to assess. It is what it is for a given engine in a given boat, and the only way to move the engine to another place is with a different prop or variable pitch prop. Prop performance data is not readily available either...I've looked. While not a design tool for a "paper" boat, what I described is a method to compare one engine to another in an existing hull. Accuracy of the prop chart for the installed engine can be judged by comparing actual fuel burn to the prop chart at a few key points. The chart for our boat is surprisingly accurate.
Nomad Willy
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Nomad Willy
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Wandering Star,
A good place to get an idea what existing boats use for power look at Yacht World. The information is however frequently supplied by the owners. You will see fuel burn quotes that are way too optimistic (low) and speeds that reflect the owners style rather than the boats capabilities.
Searching may work better using the expression "hp per ton" as I use that expression quite a bit. Obviously you can read more of what other people say about power needs than me. Sorting out all the opinions is typical of any forum.
A good place to get an idea what existing boats use for power look at Yacht World. The information is however frequently supplied by the owners. You will see fuel burn quotes that are way too optimistic (low) and speeds that reflect the owners style rather than the boats capabilities.
Searching may work better using the expression "hp per ton" as I use that expression quite a bit. Obviously you can read more of what other people say about power needs than me. Sorting out all the opinions is typical of any forum.
TDunn
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Actually it is not at all difficult to determine when a particular prop on a boat will overload the engine. The calculations are simple if a bit tedious. Here are the results for my boat, engine and prop.
The black line is the maximum power output for the engine as a function of engine rpms. The red lines (solid and dashed) are the propeller power curves for the boat for calm and rough water with my 20" diameter by 13" pitch three blade prop. The kink in the black line at about 1850 rpms is the point where the engine puts out its maximum torque (about 72 ft lbs). At 1850 the propeller curve is at about 6.2 hp and 16.5 ft-lbs of torque. The engine power curve (black line) shows that the engine can put out about 25 hp at 1850 rpms. So the boat requires a lot less than the power available at 1850 rpms.
If you increase the pitch of the prop (i.e., over prop the boat), the propeller curves (red lines) will move up and intersect the engine power curve at less than the engine's rated maximum rpms. In that case increasing the engine rpms above the intersection point of the engine and propeller curves won't generate any more speed and will make a lot of black smoke (for a diesel).
Basically, I don't see the argument for running at the rpms that correspond to the engines maximum torque output since over most of the engine's rpm range the horsepower and torque required by the prop will be considerably less than that which can be produced by the engine at full load.
Incidentally, the relationship between horsepower and torque (in ft-lbs) is:
HP = Torque x RPM ÷ 5252
Finally, it is trivial to calculate the fuel burn from the propeller curve. For my engine, fuel consumption is about 1 gallon per hour for every 16.8 hp required.For my boat the specific relationship is:
Gallons per hour = 0.05962*hp+0.054814
where hp is horsepower determined along the propeller curve.
That is determined from the engines fuel consumption curve, which is published for the engine. Even if you don't have the engines fuel consumption data, using 17-18 hp per gallon per hour of fuel consumption will get you withing 5% or so.
The black line is the maximum power output for the engine as a function of engine rpms. The red lines (solid and dashed) are the propeller power curves for the boat for calm and rough water with my 20" diameter by 13" pitch three blade prop. The kink in the black line at about 1850 rpms is the point where the engine puts out its maximum torque (about 72 ft lbs). At 1850 the propeller curve is at about 6.2 hp and 16.5 ft-lbs of torque. The engine power curve (black line) shows that the engine can put out about 25 hp at 1850 rpms. So the boat requires a lot less than the power available at 1850 rpms.
If you increase the pitch of the prop (i.e., over prop the boat), the propeller curves (red lines) will move up and intersect the engine power curve at less than the engine's rated maximum rpms. In that case increasing the engine rpms above the intersection point of the engine and propeller curves won't generate any more speed and will make a lot of black smoke (for a diesel).
Basically, I don't see the argument for running at the rpms that correspond to the engines maximum torque output since over most of the engine's rpm range the horsepower and torque required by the prop will be considerably less than that which can be produced by the engine at full load.
Incidentally, the relationship between horsepower and torque (in ft-lbs) is:
HP = Torque x RPM ÷ 5252
Finally, it is trivial to calculate the fuel burn from the propeller curve. For my engine, fuel consumption is about 1 gallon per hour for every 16.8 hp required.For my boat the specific relationship is:
Gallons per hour = 0.05962*hp+0.054814
where hp is horsepower determined along the propeller curve.
That is determined from the engines fuel consumption curve, which is published for the engine. Even if you don't have the engines fuel consumption data, using 17-18 hp per gallon per hour of fuel consumption will get you withing 5% or so.
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AusCan
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Eric - My Vetus (Mitsubishi) 42 hp has peak torque at 1750 rpm, so I would expect yours is close to the same. At that speed the engine is developing 25hp, which is enough to drive my boat at very close to hull speed in calm water.
I've still got the old prop on which is way over pitched and 1750 rpm is all I get because the torque is dropping off above that. I can still do 7 knots at 1750 rpm as it is. I'll be changing the prop next month, but will leave it slightly over pitched, to stay in the high torque range while cruising.
Have to say it again . The toque peak is at max load, far different from the prop load. Boats never use peak torque except perhaps when accelerating.
The makers say nothing about how torque varies along the prop curve.
If you want to measure the efficiency of your boat set up the only way is to measure fuel use vs distance. Just like a car MPG vs speed.
The makers say nothing about how torque varies along the prop curve.
If you want to measure the efficiency of your boat set up the only way is to measure fuel use vs distance. Just like a car MPG vs speed.
Nomad Willy
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Beat me to it bayview.
But in the bottom of the paragraph below the graphics TDunn points out that full bore and cruise are different. But then omits it later.
TDunn's post is very good and he makes a seldom understood adequately power and fuel burn function quite clear. Many fail to notice most of the curves are for maximum WOT operation. Usually leads to a lot of confusion.
But in the bottom of the paragraph below the graphics TDunn points out that full bore and cruise are different. But then omits it later.
TDunn's post is very good and he makes a seldom understood adequately power and fuel burn function quite clear. Many fail to notice most of the curves are for maximum WOT operation. Usually leads to a lot of confusion.
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AusCan
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Since I am currently way over propped, and I am only getting 1750 rpm at full throttle, wouldn't max load and prop load be the same in this particular case?
or am I not grasping this?
OP
OP
Wanderin Star
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Oh.....uhm.....thanks TD.... I see it, now....What he said!
Nomad Willy
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AusCan,
Yup .. Re #44 .. exactly.
And indeed you are WAY over propped. My max while trying a 5 blade prop was 2000rpm. Jerked the boat right out and swaped props.
I have a 2.57-1 BW gear and a 18 X 13 prop w a little too much blade area. The boat seems fine at cruise rpm (2300) and below but feels like it's a truck going up a hill at higher revs especially near a max ov 2900. The last 200 rpm comes slowly. Was not like that w the old prop. Went right up to 3000 w no struggling.
Other than a small bit of extra economy and a little less noise what's the advantage? The advantage to running at max torque seems fly stuff if meaningful at all to me.
Yup .. Re #44 .. exactly.
And indeed you are WAY over propped. My max while trying a 5 blade prop was 2000rpm. Jerked the boat right out and swaped props.
I have a 2.57-1 BW gear and a 18 X 13 prop w a little too much blade area. The boat seems fine at cruise rpm (2300) and below but feels like it's a truck going up a hill at higher revs especially near a max ov 2900. The last 200 rpm comes slowly. Was not like that w the old prop. Went right up to 3000 w no struggling.
Other than a small bit of extra economy and a little less noise what's the advantage? The advantage to running at max torque seems fly stuff if meaningful at all to me.
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AusCan
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Eric - Yes - The prop shop is recommending changing from 17x15 LH to 16 x10 RH. My new gearbox ratio is 1.94:1 which replaced the 2.34:1.
I was just getting used to operating the throttle control in reverse, so I'll have to re-learn it again.
I was just getting used to operating the throttle control in reverse, so I'll have to re-learn it again.
FF
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Beta Marine 85 HP 2,800 rpm or the optional Yanmar 110hp 3,200 rpm.
Great but at a fantastically optimistic 20hp/gal The beta will be drinking 4+gph and the Yanmar 5.5.
As you will probably be at 6 -7 mph 6K-7K for 99% of the boats cruising , the question of how to do that with efficiency remains
For most its moot as a 15% better fuel burn at 1 1/2 or 2 gpg doesn't amount to a big deal , and most tiny motors do not suffer from underloading as a more industrial engine would.
Great but at a fantastically optimistic 20hp/gal The beta will be drinking 4+gph and the Yanmar 5.5.
As you will probably be at 6 -7 mph 6K-7K for 99% of the boats cruising , the question of how to do that with efficiency remains
For most its moot as a 15% better fuel burn at 1 1/2 or 2 gpg doesn't amount to a big deal , and most tiny motors do not suffer from underloading as a more industrial engine would.
Auscan as manyboats said yes you are running at the max tated curve. Looking at the curve at that RPM will show what power and fuel you should be using.
The reason that is your max RPM is that the engine lacks extra torque to spin faster. The overload concerns become high cylinder temps due to low air flow. and possibly high exhaust temps.
Any black smoke??
The reason that is your max RPM is that the engine lacks extra torque to spin faster. The overload concerns become high cylinder temps due to low air flow. and possibly high exhaust temps.
Any black smoke??
Nomad Willy
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AusCan,
One situation where a correctly propped engine/boat combination shines is in reversing. Willy weighs 8 tons and to stop her in reverse w only a knot or two of weigh takes a bit of time w considerable throttle/rpm.
Too bad you don't have a deeper reduction. When I repowered Willy I thought of changing the gear ratio to 3-1. I have plenty of prop clearence. But w bigger props and deeper reductions have a problem related to the essence of this thread. The prop load decreases as the rpm decreases faster w a big prop so the big prop's thrust advantage is lost at lower rpm. I think that happens because of the much higher blade area of the big prop. With a small prop you have less thrust at high speeds/rpm but loose less thrust as the rpm decreases. And I suppose at some point the thrust is the same (big prop/little prop) and below that point perhaps the little prop has more thrust.
This is just my own theory and may not hold water (couldn't resist that) but a well known example of this being wide spread is outboard engines .. especially small ones. Nobody at the factory knows what boat these engines will be used on so trying to guess what prop (dia/pitch) should be employed reveals the necessity of using a prop that will present enough load to prevent the engine from over reving. The small prop becomes the answer as the load changes less up and down the rpm scale. But a big hit is taken in thrust and efficiency. But it's acceptable as the engines are light and fuel consumption small even w large inefficiency.
So w your smallish prop far less thrust is lost at cruising speed (about 50% load) than w a bigger prop at 50% load. So the inefficiency you experience is considerably less than it would seem.
However if it were my boat I'd get a lower gear and bigger prop. That said I assume you have room to swing a bigger prop w/o too little clearence to the hull. But as you point out the boat works fine. But your idle speed is probably too fast so you go in and out of gear in Harbour quite a bit and reversing probably requires more time and advanced planing.
One situation where a correctly propped engine/boat combination shines is in reversing. Willy weighs 8 tons and to stop her in reverse w only a knot or two of weigh takes a bit of time w considerable throttle/rpm.
Too bad you don't have a deeper reduction. When I repowered Willy I thought of changing the gear ratio to 3-1. I have plenty of prop clearence. But w bigger props and deeper reductions have a problem related to the essence of this thread. The prop load decreases as the rpm decreases faster w a big prop so the big prop's thrust advantage is lost at lower rpm. I think that happens because of the much higher blade area of the big prop. With a small prop you have less thrust at high speeds/rpm but loose less thrust as the rpm decreases. And I suppose at some point the thrust is the same (big prop/little prop) and below that point perhaps the little prop has more thrust.
This is just my own theory and may not hold water (couldn't resist that) but a well known example of this being wide spread is outboard engines .. especially small ones. Nobody at the factory knows what boat these engines will be used on so trying to guess what prop (dia/pitch) should be employed reveals the necessity of using a prop that will present enough load to prevent the engine from over reving. The small prop becomes the answer as the load changes less up and down the rpm scale. But a big hit is taken in thrust and efficiency. But it's acceptable as the engines are light and fuel consumption small even w large inefficiency.
So w your smallish prop far less thrust is lost at cruising speed (about 50% load) than w a bigger prop at 50% load. So the inefficiency you experience is considerably less than it would seem.
However if it were my boat I'd get a lower gear and bigger prop. That said I assume you have room to swing a bigger prop w/o too little clearence to the hull. But as you point out the boat works fine. But your idle speed is probably too fast so you go in and out of gear in Harbour quite a bit and reversing probably requires more time and advanced planing.
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The manufacturer is likely just offering you the option of what brand of engine you want. I personally do not see much difference in 85hp and 110hp. I do not know Beta Marine engines well. I do know Yanmars so I would choose the 110hp engine....strictly because it is a Yanmar...not because of the power it is making.
FF
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"I do not know Beta Marine engines well. I do know Yanmars so I would choose the 110hp engine....strictly because it is a Yanmar...not because of the power it is making."
You might consider a call to the parts dept to price different repair items.
The tractor engine will be far cheaper for parts than the Yanmar.
You might consider a call to the parts dept to price different repair items.
The tractor engine will be far cheaper for parts than the Yanmar.
Nomad Willy
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One in the Willard group and I think one or two here has Beta engines. From all the first hand stuff I hear they seem top quality. Didn't know about them when I repowered.
I had a Yanmar in my Albin and it was fine except for a sea water leak on the exhaust manifold that dripped down on the throttle shaft and I noticed a sticky throttle as corrosion set in. That experience turned me off of aluminum on the engine in contact w the coolant. That w the memories of all the corrosion on aluminum outboards.
The Yanmar was a good engine other than that little event. Started well w/o glow plugs, even in cold weather, made good power and was light. Made more noise than my Mitsu and I had some alignment issues that was probably related to the soft engine mounts and ironically had some harmonic vibration issues.
The only downside to the Beta that I can see is that it comes from the UK and dealers aren't very numerous. Both engines are what I'd call expensive.
As to what engine for the SeaPiper and the OP it should have little to do w engine brand and mostly or all to do w power. I don't know what the design speed range is for the SeaPiper. Could be that the Beta is at the lower end and the Yanmar is capable to run the boat at the high end. Or neither one has enough power or they both are too much power. In my opinion the hull design needs to be matched to the power first. Then personal preferences and cost ect can be factored in. Seems to me the boat was closer to a planing hull but I think I saw an image of some kind that showed the hull more like a slower speed SD hull. If the 85hp engine can push the boat easily throught it's design speed range I'd say go for the 85. Not many boat manufacturers offer underpowered boats so I'd bet the 85 is plenty of power and I'd recomend it.
I had a Yanmar in my Albin and it was fine except for a sea water leak on the exhaust manifold that dripped down on the throttle shaft and I noticed a sticky throttle as corrosion set in. That experience turned me off of aluminum on the engine in contact w the coolant. That w the memories of all the corrosion on aluminum outboards.
The Yanmar was a good engine other than that little event. Started well w/o glow plugs, even in cold weather, made good power and was light. Made more noise than my Mitsu and I had some alignment issues that was probably related to the soft engine mounts and ironically had some harmonic vibration issues.
The only downside to the Beta that I can see is that it comes from the UK and dealers aren't very numerous. Both engines are what I'd call expensive.
As to what engine for the SeaPiper and the OP it should have little to do w engine brand and mostly or all to do w power. I don't know what the design speed range is for the SeaPiper. Could be that the Beta is at the lower end and the Yanmar is capable to run the boat at the high end. Or neither one has enough power or they both are too much power. In my opinion the hull design needs to be matched to the power first. Then personal preferences and cost ect can be factored in. Seems to me the boat was closer to a planing hull but I think I saw an image of some kind that showed the hull more like a slower speed SD hull. If the 85hp engine can push the boat easily throught it's design speed range I'd say go for the 85. Not many boat manufacturers offer underpowered boats so I'd bet the 85 is plenty of power and I'd recomend it.
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FF
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"The only downside to the Beta that I can see is that it comes from the UK"
The ones I have seen were Kubota powered with Beta just providing marinization parts.
So replacement or repair parts for the base motor are cheap at the local lawn tractor or truck reefer shop/
The ones I have seen were Kubota powered with Beta just providing marinization parts.
So replacement or repair parts for the base motor are cheap at the local lawn tractor or truck reefer shop/
Nomad Willy
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I agree FF but at times getting on the phone and calling the people you bought the engine from for advice or parts that may need to be flown in on a small plane can be of great value. And of course over time modifications and changes are made to engines and the farm tractor store may not be able to relate completely. But the low cost route to parts can very well be to the farm tractor store. But if I'm buying anything but a crankshaft I'm going to where I bought the engine. But in defense of your post if the tractor store is close oil filters and thermostats could be bought there but you never know when there's going to be a difference in the parts.
Nomad Willy
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Baker wrote;
"I personally do not see much difference in 85hp and 110hp"
That's almost 25%. Add 25% power to my boat and it's in the "reject the engine for too much power" catergory. The engine I really wanted for Willy was a 54hp Isuzu. If you added 25% more power to a GB36 w twins it would have 300hp.
True though if you added 25% power to a typical SD trawler it wouldn't go much faster. And if you added 25% power to a FD boat most of the difference would be in it's wake.
"I personally do not see much difference in 85hp and 110hp"
That's almost 25%. Add 25% power to my boat and it's in the "reject the engine for too much power" catergory. The engine I really wanted for Willy was a 54hp Isuzu. If you added 25% more power to a GB36 w twins it would have 300hp.
True though if you added 25% power to a typical SD trawler it wouldn't go much faster. And if you added 25% power to a FD boat most of the difference would be in it's wake.
FF
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"I'm going to where I bought the engine."
Don't bother if its a Volvo. Even if its only a year or two old.
The use of a common engine is great as any changes start with a certain number , worldwide , and in many cases tractor parts are expected to be available 30-40 years later .
This can not be claimed for most marine engines.
The Ford Econo power is one exception as its one fellows business.
Try Westerbeke for 30myear old conversion parts.
Don't bother if its a Volvo. Even if its only a year or two old.
The use of a common engine is great as any changes start with a certain number , worldwide , and in many cases tractor parts are expected to be available 30-40 years later .
This can not be claimed for most marine engines.
The Ford Econo power is one exception as its one fellows business.
Try Westerbeke for 30myear old conversion parts.
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QB
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They don't have to. You can compute torque, given horsepower and RPM. TDunn gave the formula a few posts ago.
stubones99
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Part of the reason for either 1500 or 1800 RPM on some gensets is 1500 = 50hz and 1800 = 60 hz on the same windings of the generator.
You'll notice that faster turning engines have "over square" dimensions on their pistons, and need higher RPM to develop their peak power. Any engine with piston width greater than stroke is "over square" and typically a faster running engine. All the older, long stroke, under 2500 RPM engines seem to run forever if you keep them lubed.
It is my theory that the maximum efficiency "cruise" on most FD boats will be at the peak torque of the engines. Turbos tend to sway that to the upper end of the peak torque, but NA engines are most efficient at their peak torque.
