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  A Puzzle In the Making

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Author Topic:   A Puzzle In the Making
venice posted 07-24-2004 06:20 PM ET (US)   Profile for venice   Send Email to venice  
Sea trialed a 1998 DAUNTLESS with a 150-HP Ficht Engine. Prior to the sea trial, the mechanic checked the motor and found no stored codes, compression good, no problem noted. He showed me a screen on his computer with a bar graph indicating RPM as a % of total hours on the motor broken down at 1000, 2000, 3000, 4000, 5000 and 6000 RPM. Said it was unusual in that the bar graph was pretty flat at 14%-17% across the board. Advised that at 240 total hours it appeared fine but it should not be run over 5500 RPM.

When I ran the DAUNTLESS could not get over 4800 RPM according to the tachometer, which was properly set for the motor. The propeller is a 14 3/4 x 17 SS OMC Viper. Don't have a clue what kind of speed we were doing but it did not feel like 47 MPH.

Is 47-MPH about what to expect?

Is it [?] the tach, prop, or motor? Any help greatly appreciated. Thanks much, Linwood

jimh posted 07-24-2004 10:15 PM ET (US)     Profile for jimh  Send Email to jimh     
It would be very helpful if you mentioned what model of boat you are talking about.

It is frankly impossible to assess a boat's performance without accurate measurement of the boat speed. I am at a loss as to how you detected the boat's speed to be 47-MPH, or how that figure came into being.

We also need to know the gear ratio of the engine's lower unit.

Record the engine speed versus boat speed at each one-thousand RPM from 1000 upward to wide open throttle.

Performance expectations can be estimated according to the method described in the Reference section. See:

Propeller Basics: Part 2
http://continuouswave.com/whaler/reference/prop2.html

venice posted 07-24-2004 10:31 PM ET (US)     Profile for venice  Send Email to venice     
Sorry about that. It is a 1998 18' Dauntless. Got another day with the boat so I'll be able to get speeds as per your reply via gps. Did not know our max. speed. Came up with a max reasonably expected speed based on pure hearsay. First posts here and think it's a wonderful place. Thanks Much, Linwood
Plotman posted 07-24-2004 10:58 PM ET (US)     Profile for Plotman  Send Email to Plotman     
Well, if the stored data shows that the boat has run ~30 of it's life in the 5000-6000 RPM range, and the most you can get is 4800, clearly something is wrong.

The fact that the RPMs are so evenly spread out would be a red flag to me - like someone had reprogrammed the memory....

Dick posted 07-24-2004 11:07 PM ET (US)     Profile for Dick  Send Email to Dick     
Being a 1998 dauntless it must be an 18'.

My 1999 Whaler rigging chart shows running a Merc 150 Opti you use a 15.5 X 17 Mirage SS with the engine 2 holes up. I would expect the Ficht should be about equal in performance.

My 04 Evinrude brochure lists the 150 Ficht at 4750 to 5250 rpm and 150 hp @ 5000 rpm.

Buy or borrow a hand held GPS and take it for another ride.

Get some more info from the mechanic, the comment "it was pretty unsual that the bar graph was pretty flat across the board" suggests a potential problem. Have it checked by an independant shop. If the selling dealer is your only option for an engine check make sure they provide you with documentation to your satisfaction.
Not much different than buying a used car, "out the door out of my mind".

Dick

jimh posted 07-25-2004 08:34 AM ET (US)     Profile for jimh  Send Email to jimh     
I clicked my way through the BRP.COM morass to find the lower unit gear ratio of an Evinrude 150-HP Direct Injection: 1.85

The maximum RPM is 5250.

Using the Propeller Calculator (see hyperlink below) with these inputs:

SPEED = 5250
RATIO = 1.85
PITCH = 17
SLIP = 10 (reasonable number)

The Propeller Calculator computes the boat speed to be

MPH = 41

If the propeller set up is better and the SLIP is only 5%, the boat speed is 43 MPH.

The most likely reason the engine cannot turn above 4800 RPM is the propeller load is too high. If you move down to a 15-inch propeller, the engine speed should increase (according to conventional wisdom) about 400 RPM, which would then be 5200, or right at maximum rated speed. This would give you a potential boat speed of around 38 MPH.

I don't think there is any way you can get a 47-MPH hour boat out of that combination. If you want a 47-MPH boat with that hull, you will need more horsepower. How much more?

Pay attention because I'm going to show you some cool stuff here with the relationship between boat speed, boat weight, and horsepower.

We can deduce the weight from the relationship

MPH = C X SQRT(HP/WT)

thus

WT = HP/( (MPH/C)2 )

We'll use C=180, a common figure for a moderate vee hull. The rest of the data comes from your report of horsepower and maximum RPM, from which we deduced the boat speed. This is a bit of a stretch, but, this whole assessment is on shaky ground, so why not carry on. These numbers imply the boat weight in your test was about:

WT = 150 / ( (41/180)2 )

WT = 2891

If we add more horsepower, we'll add more weight, so lets say we used an engine that weights 150 pounds more, and we want the boat to go 47-MPH. Plugging these numbers into our relationship between speed, weight, and horsepower, we get:

HP = WT (MPH/C)2

HP = 3041 (47/180)2

HP = 207

So if you want a 47-MPH boat out of that Dauntless 18, you will probably need to hang a 225-HP motor on the transom.

jimh posted 07-25-2004 08:48 AM ET (US)     Profile for jimh  Send Email to jimh     
Forgot the Hyperlink to the Propeller Calculator:

Propeller Calculator
http://continuouswave.com/cgi-bin/propcalc.pl

jimh posted 07-25-2004 09:07 AM ET (US)     Profile for jimh  Send Email to jimh     
Well, I just found the information on the Boston Whaler website, www.whaler.com, and it looks like the 180 DAUNTLESS is specified for a maximum of 150-HP. Even with a big, grunty 150-HP Optimax on the transom and a $500 propeller, the engineers at Boston Whaler could not squeeze more than 43-MPH out of that hull.

Back to the boat you sea trialed:

The 1998 Ficht 150-HP Evinrude engine is now six years old. The Ficht engines have a reputation of unpredictable longevity, although the fact that this engine is still running is prima facie evidence that it is over the hurdle that killed many of its larger horsepower cousins and sent OMC into bankruptcy. However, the evil reputation of the Ficht lives after it, and the good is oft interred with their bones, as Mark Anthony might say. A buyer would be justified in demanding a price markdown for a used Ficht engine.

venice posted 07-25-2004 10:04 PM ET (US)     Profile for venice  Send Email to venice     
Thanks for all the great replies. Bought her today. Ran her for 4 hours. Ran great. The motor was recalled and apparantly the mods were effective. Anyway, hooked a gps up and observed the following:
1000 rpm 5.3 mph
2000 rpm 7.4 mph
3000 rpm 21.1 mph
4000 rpm 33.3 rpm
5150 rpm 44 mph
These readings were with motor trimmed up, 5150 rpm was best we could get. Pretty close to what feedback indicated.Thanks fellas. Still I wonder about the mechanics computer showing a history of 14% of total hours on motor at 6000 rpm. Previous owner says tach never indicated more than 5100 to 5200 rpm. and he said he did a lot of trolling making the range of rpm seen on his computer more understandable. Any replies appreciated. Anybody needing anything in my part of the world (Mississippi} don't hesitate to ask. Might even be able to hook you up with some great fishing in south La. especially Venice. Adios, Linwood
Dick posted 07-25-2004 10:20 PM ET (US)     Profile for Dick  Send Email to Dick     
venice

If you will e mail me the engine serial number I will run it through Merc dealer net and let you know what was done.
I don't go back to work untill Thu but will be back to you by Fri.

Dick

jimh posted 07-26-2004 05:24 AM ET (US)     Profile for jimh  Send Email to jimh     
Wow--those are great numbers for a six-year-old Ficht 150-HP. That motor must be making some horsepower.

You've got that OMC Viper propeller running with only 1.8% slip. That is an impressive number, too.

Any chance there were wind and current effects in those speed numbers?

Plotman posted 07-26-2004 09:48 AM ET (US)     Profile for Plotman  Send Email to Plotman     
I'd be very skeptical of reports of an even distribution across the RPM range. Who runs a boat at ~2000-2500 rpm where the boat is plowing through the water, but not really planing.
Plotman posted 07-26-2004 09:50 AM ET (US)     Profile for Plotman  Send Email to Plotman     
I'd be very skeptical of reports of an even distribution across the RPM range. Who runs a boat at ~2000-2500 rpm where the boat is plowing through the water, but not really planing.
Bigshot posted 07-26-2004 11:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Is the engine a 1998 as well? Is that a Johnson or the Evinrude in 1998? Make sure all the upgrades were done. 98 was the 2nd year of the ficht and they had multiple problems. Being she is still going strong I assume all was done and she is a good engine.
Dick posted 07-26-2004 11:43 AM ET (US)     Profile for Dick  Send Email to Dick     
venice

I meant to say I will run the number through the Bombardier system.

Dick

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