255 Conquest Re-power with SUZUKI 200 APX Twins

Optimizing the performance of Boston Whaler boats
gregdonohue
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255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Mon Feb 05, 2018 3:57 am

I'm in the process of putting twin Suzuki 200APX engines on my [255 CONQUEST].

[I am deciding between propellers with] three-blades or four-blades and their pitch.

I mainly go angling offshore at 30-miles-out and troll at 6- to 7-nautical-miles-per-hour.

Any thoughts?
Cheers Greg

jimh
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Re: Propeller Selection for 255 CONQUEST with twin 200-HP Suzuki

Postby jimh » Mon Feb 05, 2018 2:39 pm

Greg--please tell us about the engines and your engine and boat speeds.

--what is the maximum recommended engine speed range at full throttle?
--what is the maximum permitted engine speed?
--what is the gear ratio?
--what is the maximum diameter propeller that can be fitted to the engines?
--what is the typical total boat weight including all fluids, crew, gear, engines, for which you want to optimize engine operation?
--what was the prior performance of this boat with the old engines? GIve us some data about boat speed at maximum, total horsepower, and total weight under those conditions?
--how did your boat's performance compare to the published performance report from Boston Whaler?

Also, confirm the boat is a 255 CONQUEST.

Or, try the pair of propellers you have on-hand now, and let us know the performance. Give us the details of the propellers, then post engine speed and boat speed observations at various intervals of engine speed when using the propeller you have on hand. They will be a good guide to further optimization.

gregdonohue
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Mon Feb 05, 2018 10:04 pm

Thanks for you reply. The boat is a [2002] 255 CONQUEST.

The old engines were Mercury 150 OptiMax with 17-pitch propellers. Top speed was 30-nautical-miles-per-hour, [and the engine speed ] couldn't get over 5,100-RPM--over-propped in my opinion and terrible on fuel and oil.

[The 255 CONQUEST] is very heavy, I would say 3.8 te when fully loaded.

The new engines are SUZUKI 200 APX with gear ratio 2.5:1--they're being put on today.

[For new propellers] I am for sure thinking of a four-blade, either 20-pitch or 22-pitch.

Regards--Greg

gregdonohue
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Mon Feb 05, 2018 10:05 pm

Also [the 255 CONQUEST] liked to run faster; it fell off [hydroplane] around 17-nautical-miles-per-hour.

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Phil T
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby Phil T » Tue Feb 06, 2018 10:23 am

Greg--in doing some searches, I didn't find anything specific for you.

As you may know propeller selection is a bit of trial and error. For improving performance at the bottom of planing speed, a four-blade propeller will help.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

jimh
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Tue Feb 06, 2018 12:20 pm

gregdonohue wrote:...The old engines were Mercury 150 OptiMax with 17-pitch propellers. Top speed was 30-nautical-miles-per-hour, [and the engine speed ] couldn't get over 5,100-RPM...


First I will look at the horsepower and speed data, then use Crouch's method to deduce weight, assuming the hull constant is 180, which is a good guess for a Boston Whaler hull:

If 300-HP hits 30-nautical-miles-per-hour, we first convert to MPH, or 34.5; then enter into the calculator:

SPEED = 34.5
HP = 300
HULL CONSTANT = 180

The calculator computes boat weight at 8,166-lbs.

gregdonohue wrote:...[The 255 CONQUEST] is very heavy, I would say 3.8 te when fully loaded.


I am not sure what units are described by "te". If that means tonnes (or Metric ton or 2,200-lbs-per-tonne), then your estimate of weight is 8,360-lbs. That value is in close agreement with my calculated value per Crouch, a variance of only 194-lbs or 2-percent. This more or less affirms my guess at the hull constant at 180 is a good estimate--assuming the engines were making their rated 300-HP. Because they are two-stroke direct-injection engines, I would think they'd be in their rated power band at 5,100-RPM; this suggests the hull constant is a good estimate at 180.

Next I will use your value for weight to allow for a bit of weight gain when there is a re-power with larger engines, and calculate boat speed with 400-HP at 8,360-lbs with hull constant 180. Crouch's method returns an estimate of boat speed to be 39-MPH. (That would be 33.9-nautical-miles-per-hour.)

Now we can look at propeller pitch. We need the gear ratio; you say 2.5:1 and I will use that. We also need the recommended full-throttle engine speed. Since the new engines are four-stroke-power-cycle engines, they probably like to rev-up quite a bit, so I will use 6,000-RPM at the high end of the full-throttle range. Now we can calculate a propeller pitch based on

ENGINE RPM = 6000
GEAR RATIO = 2.5
SPEED = 39-MPH
SLIP = 9 (which is a nice average for good propellers operating at their design speeds)

The pitch calculates to 18.8 or 19-pitch

gregdonohue wrote:[For new propellers] I am for sure thinking of a four-blade, either 20-pitch or 22-pitch.


I think your estimate of 22-pitch is going to be too high. In order for the engines to be able to accelerate to 6,000-RPM with 22-pitch propellers, the boat speed would be about 46-MPH. That is a lot faster than I would expect, based on your prior performance. To get 46-MPH with 400-HP and this weight suggests that the hull constant must be around 210. I don't think a hull constant of 210 is likely for a Boston Whaler Accu-track hull, but it might be possible. The earlier calculation might have been off because your twin 150-HP engines were never up to speed and making their rated horsepower. I will be surprised if you could spin 22-pitch and hit 46-MPH (or 40-nautical-miles-per-hour) with the new twin 200-HP engines. Of course, actual testing will give us the actual answer.

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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Tue Feb 06, 2018 12:42 pm

gregdonohue wrote:......[and the engine speed ] couldn't get over 5,100-RPM--over-propped in my opinion...


A good indication of proper propeller selection is given by observing the highest speed the engine can accelerate to compared with its rated highest speed. If you want to avoid being "over-propped" you should aim for a propeller pitch that lets the engines accelerate right to the top end of the recommended full-throttle range. I looked up some specifications for the SUZUKI 200AP engine:

http://www.suzukimarine.com/~/media/Mar ... A%20v4.pdf

I found the maximum engine speed was 6,100-RPM. If you want a propeller that gives you the feeling of avoiding engine lugging, allows rapid acceleration, and makes the engine happy, go for a propeller pitch that let's the engine run up to almost 6,100-RPM at full throttle with your typical weight load.

To get a better understanding of how propeller pitch affects acceleration, read my article

Propeller Power Curve
Computing the load of a propeller

http://continuouswave.com/whaler/reference/propellerPowerCurve.html

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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Tue Feb 06, 2018 5:19 pm

As for suggestions of specific propellers, I recommend you test some Evinrude REBEL propellers. The REBEL propeller is the most FUEL EFFICIENT propeller that I have tested. The classic three-blade design gives very good all-round performance, fuel economy, and speeds.

The Evinrude REBEL TBX propeller uses a universal hub and bushing design called the TBX bushing. I have compared the TBX hub and bushing design to other choices and found it offers more positive connection between propeller shaft, bushing, hub, and propeller than other designs due to the longer length of the contact area.

Here is a look at the TBX bushing design (shown with a four-blade CYCLONE propeller):

Image

Note the long metal coupling between the propeller shaft and the bushing; the length of this component is much longer than on other brands which offer similar universal systems.

The Evinrude interchangeable TBX hub kit is designed to also fit Mercury, Yamaha, Honda, and Suzuki V6 outboard engines. For example, for Suzuki you would use the following components:

128775 Thrust Washer (stock part for all)
128752 Torsion Bushing (stock part for all)
177289 Bushing Sleeve (stock part for all)
128765 Spacer (specifically for Suzuki)

For the propeller nut you will use the one supplied with your Suzuki engines. You can order all the parts under one part number, 177288. The kit has all the parts for any Mercury, Yamaha, Honda, and Suzuki V6 outboard engines to use a TBX propeller from Evinrude.

The REBEL TBX propeller is available in pitches of 15, 17, 18, 19, 20, 21, 22, 23, and 25, and in both right-hand and left-hand rotation. (Here I assume you will get counter-rotating twin engines.) You can really dial-in the right pitch when working with a propeller line that has pitch increments of 1-inch.

If you really want a four-blade, try the Evinrude CYCLONE four-blade. I have also tested that propeller. The CYCLONE TBX propeller is available in pitches of 15, 17, 18, 19, 20, 21, and 23, and in both right-hand and left-hand rotation.

EVINRUDE has published a really good booklet that explains propellers and how to select them. It is free and can be downloaded from:

http://www.operatorsguides.brp.com/OperatorsGuidesAttachments/OwnersManuals_EJ/attach/Accessories%5C766315%20EN.pdf

I think you will find this Evinrude publication has a lot of good information about propellers.

For more about the REBEL Propeller, see:
http://continuouswave.com/ubb/Forum4/HTML/004368.html

For some first-hand test data from my own testing of the REBEL and CYCLONE propellers, see

REVENGE 22 W-T WD with 225-HP, Three Propellers
http://continuouswave.com/ubb/Forum4/HTML/006964.html

gregdonohue
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Wed Feb 07, 2018 12:58 am

WOW--Thank you so much for the detailed replies.

The on-water test is tomorrow.

Yes, the engines are counter rotating engines. These can either spin-in or spin-out
Going for the traditional "out first up."

I will post up the results later.

Many thanks

gregdonohue
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Wed Feb 07, 2018 1:54 am

The props we are testing are:

--Suzuki 4 x 15 x 20
--Suzuki 3 x 16 x 21

So your thoughts are correct: 22-pitch might be too big.

Cheers Greg

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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Wed Feb 07, 2018 11:03 pm

If you have those Suzuki engines which can be flipped to counter-rotation from standard rotation or vice versa with a software setting, that will add all sorts of fun to the propeller testing, as now you can easily compare the rotation settings and transom position without having to physically move the engines on the transom--you just have to switch the propellers between the engines and then flip the engine rotation.

And don't forget about TOE-IN and TOE-OUT. For some advice on that, see

Twin Engine Installation On Moderate V-hull Boats
http://continuouswave.com/whaler/refere ... nting.html

and don't miss:

http://continuouswave.com/ubb/Forum4/HTML/001476.html

You might also consider letting the engines decide the TOE-IN or TOE-OUT by loosening the tie bar on one engine and letting it find its own groove. See

http://continuouswave.com/ubb/Forum4/HTML/004507.html

gregdonohue
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Thu Feb 08, 2018 6:34 am

This morning, first run with the 20-pitch:
--fantastic [acceleration]
--top speed 39-nautical-miles-per-hour
--engine over-rev

Tomorrow will try out 22-pitch ([Vendor] sent a 22 and a 18 instead of a pair of 22's}

We did take it out with a 20 and a 22; the engine with the 22 was hitting 5,950-RPM; 22-pitch should be spot on.

Cheers Greg

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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Thu Feb 08, 2018 8:30 am

Propeller Calculator Data Input
MPH = 44.8 (39-nautical-miles-per-hour observed)
PITCH = 20
RATIO = 2.5
SLIP = 9

This calculates RPM over 6,500-RPM.

I am very impressed the Suzuki 200-HP engines can turn the 20-pitch that fast.

Prediction for 22-pitch:

Propeller Calculator Data Input
PITCH = 22
RATIO = 2.5
SLIP = 9
RPM = 5900 (observed)

This calculates boat speed 45-MPH, or 39.1-nautical-miles-per-hour.

gregdonohue
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby gregdonohue » Sun Feb 11, 2018 3:45 am

[T]ook out the [255 CONQUEST] today with five adults and a small child onboard.

The [twin Suzuki 200 APX engines accelerated to] 5,800-RPM.

Top [boat] speed was 37-nautical-miles-per-hour into an [opposing current from] tide.

I am very happy with the performance of the 15-1/4 x 22-pitch four-blade propeller.

[Fuel flow rate while] cruising at 25-nautical-miles-per-hour was 45-liter per hour.

Great [acceleration onto plane from a standing start] .

Cheers

jimh
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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Sun Feb 11, 2018 10:09 am

Checking on your performance data with the propeller calculator:

RPM = 5800
RATIO = 2.5
PITCH = 22
SPEED = 42.5 (MPH, equivalent of 37-nautical-miles-per-hour)

Calculated SLIP = 12

Those data sound reasonable.

Checking on your fuel economy data with conversion into units more familiar to all readers here in North America:

SPEED = 28.7 MPH
Flow rate = 11.9 GPH
Fuel Economy = 2.4-MPG

The fuel economy sounds really rather good for a 25-foot boat with a heavy load and a moderately deep V-hull.

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Re: 255 Conquest Re-power with SUZUKI 200 APX Twins

Postby jimh » Sun Feb 11, 2018 10:51 am

In regard to the propeller pitch selection, recall that the only data point was the boat could hit 30-nautical with 300-HP.

We analyze this on the basis that for a moderate planing hull the boat speed on plane will be proportional to the power-to-weight ratio to the 0.5 exponent (square root). If we assume no weight change, then boat speed ratio is proportional to horsepower ratio to the 0.5-exponent:

SPEED RATIO = POWER RATIO0.5

To find speed expected with 400-HP based on speed reached with 300-HP we find the new speed from

Speed-with-400-HP = Speed-with-300-HP × (400/300)0.5
Speed-with-400-HP = 34.6

With 34.6-nautical as the predicted speed, the appropriate propeller pitch would be 20-pitch

The observed speed with 400-HP is now reported to be 37-nautical with the propeller at 22-pitch.

There are several possible reasons for the discrepancy:

--Crouch's formula is wrong; not likely
--there was a weight change that was unaccounted for; likely
--one (or both) of the horsepower figures is wrong; not likely
--the initial set-up of propeller and engine was not optimized and the new set-up is much better; likely