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Author Topic:   Honda BF130 WOT Engine Speed

Matt F posted 08-11-2010 12:19 PM ET (US)
I am concerned that my 2002 Honda BF130 may be slightly over-propped. The manual says that the acceptable RPM range is 5,000 to 6,000-RPM. My motor is running at about 5,250-RPM WOT typically loaded. It cruises nicely anywhere in between 3,000 and 4,000-RPM. I run the motor over 4,000-RPM only occasionally to stretch its legs a bit. If it matters, the gear ratio is 2.00:1 (28/14).
I’m very pleased with the performance, I just want to make sure that we’re not making the motor work harder than it should. I’d assume that being within the acceptable RPM range is good, but it seems like a lot of people suggest that you should really want to be in the mid to upper end of spectrum to ensure longevity.
As always, any input is welcome.
Tohsgib posted 08-11-2010 12:42 PM ET (US)
What does she run full tilt boogey with light load?
I personally would like to see it up at 5600+ with typical load. My Suzuki 115 runs about 5900 light and 5600 with heavy load and redline is the same. I think my engine states 5k-6k as well.
Matt F posted 08-11-2010 02:54 PM ET (US)
Tohsgib: I’ll have to validate this, but I don’t think it is too much more — maybe 5400. I’ll take a look this weekend and get back to you. The boat rarely sees coolers full of ice or heavy dive equipment — more likely are one or two adults and a few kids. Perhaps the larger issue in terms of load is the build-up of several layers of old (hard) bottom paint. One of those things I know I need to get to, but also one of those things that is easily put off just one more year.
tedious posted 08-12-2010 08:10 AM ET (US)
If it were me, I'd be looking to come down a couple of inches in pitch - I think it's better for all motors to be right up close to the redline when lightly loaded. If you ever do run with a heavy load and you're current setup, you're likely to be under 5K, which is not great.
But since props are expensive, if you've been running this way for a while, you might want to fix your bottom paint situation as the first step in the experiment.
Tim
HawaiianWhaler posted 08-12-2010 08:28 AM ET (US)
Matt F - It might help folks to give you relevant performance if you tell us what model Whaler you have and what diameter and pitch prop you have. For example, my BF130 delivers 5700 RPM at WOT using a 3x13.75x13 prop to push my Conquest 21.
jimh posted 08-13-2010 07:45 AM ET (US)
If you changed the propeller to one with 2-inch lower pitch, you would probably pick up about 400 to 500-RPM in engine speed. I am guessing you might have a 19-pitch propeller now. This implies a boat speed of about
RPM = 5250
RATIO = 2.0
PITCH = 19
SLIP = 10 (estimate)
MPH = 42.5
With lower pitch and more engine speed, we could calculate the boat speed as
RPM = 5750
RATIO = 2.0
PITCH =17
SLIP = 10
MPH = 41.6
The actual results may be slightly different, as the SLIP could be a factor in both calculations.
jimh posted 08-13-2010 08:18 AM ET (US)
Running a propeller with less pitch makes the propeller easier for the engine to turn. For each propeller pitch there is a corresponding curve of propeller power needed to turn it. Some graphs of propeller power curves are shown in an article I wrote in the REFERENCE section at
Propeller Power Curve
http://continuouswave.com/whaler/reference/propellerPowerCurve.html
At a given engine speed, the more power available from the engine relative to the power needed by the propeller to be turned at a higher speed becomes an indication of how easily the engine can accelerate. In the optimum set-up the engine power curve and the propeller power curve will meet at the maximum engine speed permitted. If too much propeller pitch is used, the engine runs out of power before reaching its maximum engine speed.
With four-cycle engines it is common that the maximum horsepower occurs close to the maximum engine speed. Below is a graph of engine power as a function of engine speed for three different engines. As you can see, in some cases the four-cycle engines do not reach their rated horsepower output until they are running at their maximum rated speed or very close to it.
This explains why so often there is a recommendation to select a propeller that allows the engine to run to maximum speed. If running a propeller with more pitch you will generally have slower acceleration, however, you may get slightly better fuel economy at mid-range cruise.
Tohsgib posted 08-13-2010 11:20 AM ET (US)
Jim...you "might" not get better economy @ cruise with a bigger prop depending on setup. If the engine is slightly straining at 4k to run 25mph with a 19", it might be under less stress at 4200 with a 17" to run the same 25mph. Only testing will give you the correct answer. Luckily a Honda uses a Merc prop which you should easily be able to borrow from somebody. I am not so lucky with my 115 Suzuki. Luckily my friend went larger on his 115 and I bought his 22 and sold my 20 which was a tad too small. We bought them the same day so they were both like new.
Matt F posted 08-13-2010 12:35 PM ET (US)
Jim:
Your last point interests me in a sort of “who wouldn’t want better fuel economy” sort of way. Like everything, I’m sure it comes in a a series of tradeoffs. I am perfectly willing to lose top-end performance for better economy. I am not, however, willing to gain better economy at the expense of working an engine too hard. I guess the question is where that line lies, eh?
A caveat — the boat in question is not a Whaler — it is not even close. But, I thought the over-riding question was general enough that it passed muster in terms of posting on this site. The hull in question is of the semi-displacement, “soft chine” variety. It is an Easter 24, Center Console with the following specs:
Length Over All: 23’ 6”
Draft: 1’3”
Beam: 7’8”
Weight: 1830
As it is not really a planing hull, there is virtually no strain in getting over the hump. One of the things that has pleased me most is that it really doesn’t lug at any RPM. It also doesn’t go that fast — just over 30mph on the GPS wide open.
I’ve thought about posting my thoughts on the boat in the GAM, but it just struck even me as being too far off topic. That said, for whomever cares, it is exactly what they say: smooth, efficient & easy on the eye (at least mine). It is also can be wet and a little squirrely in a following sea. It also doesn’t have an ounce of foam in it... That doesn’t bother me, but I can imagine that it would be a deal-breaker for 95% of the folks here.
Tohsgib posted 08-13-2010 12:46 PM ET (US)
My friend had a 22 Eastern cabin with a 90 OMC on it. Thing did like 30+ but yes she was wet. Cool boat in the Cape, don't see many down in FL. Being that hull, I would try and see what you are getting and try to get closer to 6k. Like I said above...5800 light load and say 5400 loaded will be a good mark. If you are getting 5600 now FTB, I would just have the prop tweaked over the winter for $50 and fetch another couple hundred rpm.
Matt F posted 08-13-2010 01:41 PM ET (US)

I find the Propeller Power Curve challenging. I think I understand the broad strokes, but won’t even begin to pretend to understand how you go there. It does seem like I am optimized to get very good fuel economy. And while I don’t have a fuel flow meter installed (yet), I can say that in an anecdotal sense, my brother and I are slack-jawed at how miserly the outfit is. The other side of the coin would seem to be that we don’t have much by way of reserve power. From your graphs, it would appear my reserve/gray area would be pretty slim.
The prop on there now is aluminum, so I think it would be more a matter of buying something new — and perhaps a larger can of worms altogether...
Tohsgib posted 08-13-2010 01:48 PM ET (US)
No brainer then(pretty much) go for a SS prop one size smaller than you have. I thought all Hondas came with a SS prop.
Matt F posted 08-13-2010 02:00 PM ET (US)
Now I am going past the general question that I could reconcile posting on a Whaler site... Any thoughts on a good fit for that boat/motor set up. Top speed is not the goal, just something that is the right fit for the motor/hull.
Thanks for taking the time.
Tohsgib posted 08-13-2010 02:29 PM ET (US)
Yeah..2" lower in pitch SS prop than what you have now in Alum. If you have a 17" go with a 15" SS.
Tohsgib posted 08-13-2010 02:30 PM ET (US)
How high is engine mounted?
Matt F posted 08-13-2010 03:05 PM ET (US)
I’m embarrassed to say that I don’t know. I’ll take a look this weekend and post both the prop specs and how many holes up it is. I never really meant to take this past the general theory of it all. Thanks for entertaining it.
Matt F posted 08-15-2010 12:38 PM ET (US)
The propeller appears to be a three-blade Honda/Solas 13.5x15. The motor is on the first (lowest) hole.
This morning I looked at the WOT reading and it was right at 5250 with a light-ish load. Granted. it was into the wind with the dodger up and going over some nice swell action.
Would reducing the diameter by 1/4" be another approach to gain a few RPMs?
Thanks for your help, Matt
Tohsgib posted 08-15-2010 01:54 PM ET (US)
No...diameter has little to do with it. Raise the engine up 2 holes and get a 13" SS prop.
Matt F posted 12-06-2010 09:48 AM ET (US)
I am reviving this old thread as I think I may have found a propeller that fits the bill. Would a 13.25x13 Honda Turbo get me closer to the optimal WOT rpms? It would seem so from Tohsgib’s last post, but I’d hate to buy one and regret it later. I guess my concern would be that the slight reduction in both diameter and pitch would be negated by superior design/materials resulting in some sort of diminished slip or some sort of increased efficiencies. Just don’t want to make a several hundred dollar mistake. Prop selection seems like the intersection of advanced physics and voodoo to me.
Hope this isn’t bad form in reviving a thread that is several months — thought the back story might help.

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Author	Topic: Honda BF130 WOT Engine Speed
Matt F	posted 08-11-2010 12:19 PM ET (US) I am concerned that my 2002 Honda BF130 may be slightly over-propped. The manual says that the acceptable RPM range is 5,000 to 6,000-RPM. My motor is running at about 5,250-RPM WOT typically loaded. It cruises nicely anywhere in between 3,000 and 4,000-RPM. I run the motor over 4,000-RPM only occasionally to stretch its legs a bit. If it matters, the gear ratio is 2.00:1 (28/14). I’m very pleased with the performance, I just want to make sure that we’re not making the motor work harder than it should. I’d assume that being within the acceptable RPM range is good, but it seems like a lot of people suggest that you should really want to be in the mid to upper end of spectrum to ensure longevity. As always, any input is welcome.
Tohsgib	posted 08-11-2010 12:42 PM ET (US) What does she run full tilt boogey with light load? I personally would like to see it up at 5600+ with typical load. My Suzuki 115 runs about 5900 light and 5600 with heavy load and redline is the same. I think my engine states 5k-6k as well.
Matt F	posted 08-11-2010 02:54 PM ET (US) Tohsgib: I’ll have to validate this, but I don’t think it is too much more — maybe 5400. I’ll take a look this weekend and get back to you. The boat rarely sees coolers full of ice or heavy dive equipment — more likely are one or two adults and a few kids. Perhaps the larger issue in terms of load is the build-up of several layers of old (hard) bottom paint. One of those things I know I need to get to, but also one of those things that is easily put off just one more year.
tedious	posted 08-12-2010 08:10 AM ET (US) If it were me, I'd be looking to come down a couple of inches in pitch - I think it's better for all motors to be right up close to the redline when lightly loaded. If you ever do run with a heavy load and you're current setup, you're likely to be under 5K, which is not great. But since props are expensive, if you've been running this way for a while, you might want to fix your bottom paint situation as the first step in the experiment. Tim
HawaiianWhaler	posted 08-12-2010 08:28 AM ET (US) Matt F - It might help folks to give you relevant performance if you tell us what model Whaler you have and what diameter and pitch prop you have. For example, my BF130 delivers 5700 RPM at WOT using a 3x13.75x13 prop to push my Conquest 21.
jimh	posted 08-13-2010 07:45 AM ET (US) If you changed the propeller to one with 2-inch lower pitch, you would probably pick up about 400 to 500-RPM in engine speed. I am guessing you might have a 19-pitch propeller now. This implies a boat speed of about RPM = 5250 RATIO = 2.0 PITCH = 19 SLIP = 10 (estimate) MPH = 42.5 With lower pitch and more engine speed, we could calculate the boat speed as RPM = 5750 RATIO = 2.0 PITCH =17 SLIP = 10 MPH = 41.6 The actual results may be slightly different, as the SLIP could be a factor in both calculations.
jimh	posted 08-13-2010 08:18 AM ET (US) Running a propeller with less pitch makes the propeller easier for the engine to turn. For each propeller pitch there is a corresponding curve of propeller power needed to turn it. Some graphs of propeller power curves are shown in an article I wrote in the REFERENCE section at Propeller Power Curve http://continuouswave.com/whaler/reference/propellerPowerCurve.html At a given engine speed, the more power available from the engine relative to the power needed by the propeller to be turned at a higher speed becomes an indication of how easily the engine can accelerate. In the optimum set-up the engine power curve and the propeller power curve will meet at the maximum engine speed permitted. If too much propeller pitch is used, the engine runs out of power before reaching its maximum engine speed. With four-cycle engines it is common that the maximum horsepower occurs close to the maximum engine speed. Below is a graph of engine power as a function of engine speed for three different engines. As you can see, in some cases the four-cycle engines do not reach their rated horsepower output until they are running at their maximum rated speed or very close to it. This explains why so often there is a recommendation to select a propeller that allows the engine to run to maximum speed. If running a propeller with more pitch you will generally have slower acceleration, however, you may get slightly better fuel economy at mid-range cruise.
Tohsgib	posted 08-13-2010 11:20 AM ET (US) Jim...you "might" not get better economy @ cruise with a bigger prop depending on setup. If the engine is slightly straining at 4k to run 25mph with a 19", it might be under less stress at 4200 with a 17" to run the same 25mph. Only testing will give you the correct answer. Luckily a Honda uses a Merc prop which you should easily be able to borrow from somebody. I am not so lucky with my 115 Suzuki. Luckily my friend went larger on his 115 and I bought his 22 and sold my 20 which was a tad too small. We bought them the same day so they were both like new.
Matt F	posted 08-13-2010 12:35 PM ET (US) Jim: Your last point interests me in a sort of “who wouldn’t want better fuel economy” sort of way. Like everything, I’m sure it comes in a a series of tradeoffs. I am perfectly willing to lose top-end performance for better economy. I am not, however, willing to gain better economy at the expense of working an engine too hard. I guess the question is where that line lies, eh? A caveat — the boat in question is not a Whaler — it is not even close. But, I thought the over-riding question was general enough that it passed muster in terms of posting on this site. The hull in question is of the semi-displacement, “soft chine” variety. It is an Easter 24, Center Console with the following specs: Length Over All: 23’ 6” Draft: 1’3” Beam: 7’8” Weight: 1830 As it is not really a planing hull, there is virtually no strain in getting over the hump. One of the things that has pleased me most is that it really doesn’t lug at any RPM. It also doesn’t go that fast — just over 30mph on the GPS wide open. I’ve thought about posting my thoughts on the boat in the GAM, but it just struck even me as being too far off topic. That said, for whomever cares, it is exactly what they say: smooth, efficient & easy on the eye (at least mine). It is also can be wet and a little squirrely in a following sea. It also doesn’t have an ounce of foam in it... That doesn’t bother me, but I can imagine that it would be a deal-breaker for 95% of the folks here.
Tohsgib	posted 08-13-2010 12:46 PM ET (US) My friend had a 22 Eastern cabin with a 90 OMC on it. Thing did like 30+ but yes she was wet. Cool boat in the Cape, don't see many down in FL. Being that hull, I would try and see what you are getting and try to get closer to 6k. Like I said above...5800 light load and say 5400 loaded will be a good mark. If you are getting 5600 now FTB, I would just have the prop tweaked over the winter for $50 and fetch another couple hundred rpm.
Matt F	posted 08-13-2010 01:41 PM ET (US) I find the Propeller Power Curve challenging. I think I understand the broad strokes, but won’t even begin to pretend to understand how you go there. It does seem like I am optimized to get very good fuel economy. And while I don’t have a fuel flow meter installed (yet), I can say that in an anecdotal sense, my brother and I are slack-jawed at how miserly the outfit is. The other side of the coin would seem to be that we don’t have much by way of reserve power. From your graphs, it would appear my reserve/gray area would be pretty slim. The prop on there now is aluminum, so I think it would be more a matter of buying something new — and perhaps a larger can of worms altogether...
Tohsgib	posted 08-13-2010 01:48 PM ET (US) No brainer then(pretty much) go for a SS prop one size smaller than you have. I thought all Hondas came with a SS prop.
Matt F	posted 08-13-2010 02:00 PM ET (US) Now I am going past the general question that I could reconcile posting on a Whaler site... Any thoughts on a good fit for that boat/motor set up. Top speed is not the goal, just something that is the right fit for the motor/hull. Thanks for taking the time.
Tohsgib	posted 08-13-2010 02:29 PM ET (US) Yeah..2" lower in pitch SS prop than what you have now in Alum. If you have a 17" go with a 15" SS.
Tohsgib	posted 08-13-2010 02:30 PM ET (US) How high is engine mounted?
Matt F	posted 08-13-2010 03:05 PM ET (US) I’m embarrassed to say that I don’t know. I’ll take a look this weekend and post both the prop specs and how many holes up it is. I never really meant to take this past the general theory of it all. Thanks for entertaining it.
Matt F	posted 08-15-2010 12:38 PM ET (US) The propeller appears to be a three-blade Honda/Solas 13.5x15. The motor is on the first (lowest) hole. This morning I looked at the WOT reading and it was right at 5250 with a light-ish load. Granted. it was into the wind with the dodger up and going over some nice swell action. Would reducing the diameter by 1/4" be another approach to gain a few RPMs? Thanks for your help, Matt
Tohsgib	posted 08-15-2010 01:54 PM ET (US) No...diameter has little to do with it. Raise the engine up 2 holes and get a 13" SS prop.
Matt F	posted 12-06-2010 09:48 AM ET (US) I am reviving this old thread as I think I may have found a propeller that fits the bill. Would a 13.25x13 Honda Turbo get me closer to the optimal WOT rpms? It would seem so from Tohsgib’s last post, but I’d hate to buy one and regret it later. I guess my concern would be that the slight reduction in both diameter and pitch would be negated by superior design/materials resulting in some sort of diminished slip or some sort of increased efficiencies. Just don’t want to make a several hundred dollar mistake. Prop selection seems like the intersection of advanced physics and voodoo to me. Hope this isn’t bad form in reviving a thread that is several months — thought the back story might help.