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  23 Walkaround Hull Form and Speeds with Various Horsepower

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Author Topic:   23 Walkaround Hull Form and Speeds with Various Horsepower
acseatsri posted 05-13-2015 10:25 PM ET (US)   Profile for acseatsri   Send Email to acseatsri  
Tuesday, for the first time, I was out [in a Boston Whaler 23 WALKAROUND boat] with twin 150-HP Johnson Oceanrunners, and [the top speed was] 47-MPH. [Calculating the total weight of the boat] based on published numbers:

4050-lbs Hull
780-lbs engines
450-lbs for 70 gallons gasoline figured as 6.5-lbs/gallon
120-lbs batteries
50-lbs propellers and oil tanks
400-lbs for two people

Making 5,850-lbs the calculated total weight. [jimh's] Crouch's Calculator says 207.5 hull factor. Based on this figure, a single 250-HP should push the 23 WALKROUND to 42.9-MPH. Unfortunately, Honda has an XXL driveshaft on back order until June 1, 2015, so it'll be a while before I get to test the numbers.

I had no problems at all backing [the Boston Whaler 23 WALKAROUND] into the slip on one engine.

Also, couldn't get speed runs in both directions due to somewhat sloppy conditions, but it was slack tide.

Jeff posted 05-13-2015 11:00 PM ET (US)     Profile for Jeff  Send Email to Jeff     
Sounds close to our the numbers we see with our 23 Walkaround WhalerDrive model with twin Yamaha 150's (1900+ hours). We see 46.7 as a WOT.
jimh posted 05-14-2015 01:18 AM ET (US)     Profile for jimh  Send Email to jimh     
If any boat goes 47-MPH with 300-HP, you can calculate the speed with 250-HP without much fuss by just assuming the weight remains constant. The new speed is just the ratio of the horsepower to the 0.5 exponent times the original speed. In this case

(250/300)^0.5 x 47-MPH = 42.9

You don't need the weight, the hull constant calculation, or my implementation of George Crouch's theory in the form of a handy calculator to get that new speed figure.

jimh posted 05-14-2015 10:55 AM ET (US)     Profile for jimh  Send Email to jimh     
As a comparison, let me offer some data I observed with my 1990 Boston Whaler REVENGE 22 W-T Whaler Drive boat. With 225-HP, the top speed is 41-MPH. The boat weight was estimated to be about 3730-lbs and the measured weight was calculated to be about 4,130-lbs. Added to that was about 570-lbs of crew, fuel, and gear, giving a total weight of 4,800-lbs. In summary, the data for calculating the hull constant of this boat would be

LBS = 4800
HP = 225
MPH = 41

Those data produce a hull factor of 189. There seems to be a general trend for the classic Boston Whaler moderate V-hull boats to calculate to a hull factor in the 180 to 190 range.

My data comes from http://continuouswave.com/whaler/reference/propellerWDSingle.html which has a summary of many propeller tests and some actual scale weights.

jimh posted 05-14-2015 10:55 AM ET (US)     Profile for jimh  Send Email to jimh     
Calculating the hull factor according to naval architect George Crouch's method for estimating the speed of moderate planing hulls based on weight and horsepower is an interesting exercise. The hull factor is based on the relationship of boat speed to the horsepower-to-weight ratio.

A Boston Whaler 23 WALKAROUND hull has a rather fine entry forward and then a decreasing deadrise toward the stern, but there is still enough deadrise at the transom that I'd characterize it certainly as a V-hull boat, and perhaps a deeper V-hull than a classic Boson Whaler boat would have for that length. The boat speed data (given above by ACSEATRI) sound good, and the speed is affirmed by very similar data from Jeff's boat with the same engine power. The horsepower data is reasonable, based on the engine ratings and the assumption the propellers are selected to allow the engine to accelerate to its full-throttle recommended speed range. The weight data is probably the most likely to have some variance, but ACSEATRI's estimates seem reasonable. In any case, boats probably tend to weigh more than one might think, and if the weight were too low it would tend to hold the hull factor down, not inflate it. I don't see any of the weights as being over-estimated. The weight I am not familiar with is the hull weight, but I assume, as mentioned, it comes from some published weight by Boston Whaler.

I am surprised by the hull factor of 207.5. I would have thought the 23 WALKAROUND hull would have a lower hull factor, based on the deeper V-hull design. It seems to be easily driven when on plane. I guess the hull form must have good lifting force, and it can get on plane and run quite efficiently. Thanks for sharing the data.

jimh posted 05-14-2015 12:04 PM ET (US)     Profile for jimh  Send Email to jimh     
Does the 23 WALKAROUND whose speed data we are discussing have the Whaler Drive option?
acseatsri posted 05-14-2015 07:38 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
My [Boston Whaler 23 WALKAROUND] boat is the standard notched transom and has no Whaler Drive. The engines are turning 14.5 x 19 stainless propellers of unknown manufacturer, and the engines revved to 5500 to 5600-RPM at WOT. I suspect there is more speed to be had if it weren't for the choppiness of the water which didn't allow me to fully trim out for maximum speed.

The dead rise at the stern is 20-degrees--measured accurately because I mounted a side scan transducer on the bottom of the hull with a fairing block to make the transducer level. This is the first time I've ever been able to see both left and right with the side scan without tilting the engine nearly all the way out of the water. Maybe one of these days we'll get a calm day and I can do a real speed run to confirm my preliminary numbers.

acseatsri posted 05-14-2015 08:08 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
One other observation: on a classic Outrage 22, the V-hull remains sharp all the way from the bow to the stern. On both the 21 WALKAROUND and 23 WALKAROUND, the V-hull transitions from a sharp Vee at the bow to a rather large radius at the stern. This may provide the additional lift that increases the hull constant factor.
jimh posted 05-15-2015 07:14 AM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the additional data on the hull form. A deadrise at the transom of 20-degrees is still a rather sharp V-hull. The deadrise at the transom of a classic OUTRAGE 22-foot hull is less, probably about 16-degrees.
Jeff posted 05-15-2015 11:36 AM ET (US)     Profile for Jeff  Send Email to Jeff     
Here are a few images that show the hull form of a 23 Walkaround.

Bow
http://img.photobucket.com/albums/v427/jeff_rohlfing/ 1993%2023%20Boston%20Whaler%20Walkaround%20Whalerdrive/ 23walkaround_82013_selects-22_zps17ec5145.jpg

Under the hull
http://img.photobucket.com/albums/v427/jeff_rohlfing/ 1993%2023%20Boston%20Whaler%20Walkaround%20Whalerdrive/ 23walkaround_82013_selects-3_zps5c488366.jpg

Stern
http://img.photobucket.com/albums/v427/jeff_rohlfing/ 1993%2023%20Boston%20Whaler%20Walkaround%20Whalerdrive/ 23walkaround_82013_selects-111_zps81acd615.jpg

Side Profile. In this image the two red lines are parallel and the yellow line follows the hull bottom / Keel line.
http://img.photobucket.com/albums/v427/jeff_rohlfing/ 1993%2023%20Boston%20Whaler%20Walkaround%20Whalerdrive/ 23walkaround_82013_selects-122_zps66rj5ntp.jpg
http://img.photobucket.com/albums/v427/jeff_rohlfing/ 1993%2023%20Boston%20Whaler%20Walkaround%20Whalerdrive/ 23walkaround_82013_selects-122_zps387c13d8.jpg

Jeff posted 05-15-2015 11:37 AM ET (US)     Profile for Jeff  Send Email to Jeff     
It should be noted that this same exact hull form is used on the Post Classic 24 Outrage.
Peter posted 05-16-2015 06:12 AM ET (US)     Profile for Peter  Send Email to Peter     
Besides the rounded profile for the V in the stern, the AccuTrak hull does not have sponsons, unlike the classic 18 to 27 foot V hull Whalers. While those sponsons help with tracking and stability, they do so at the expense of more drag. Those sponsons plus the sharp V contribute to the lower Crouch factor.
jimh posted 05-16-2015 10:19 AM ET (US)     Profile for jimh  Send Email to jimh     
Thanks to Jeff for the nice gallery of images of the hull form of the Boston Whaler 23 WALKAROUND. I had not realized the hull form was so rounded in the stern.

Also thanks to Peter for pointing out the lack of the runners or sponsons in this hull. That is another significant difference in this hull from the classic Boston Whaler hull.

jimh posted 05-16-2015 10:29 AM ET (US)     Profile for jimh  Send Email to jimh     
I noticed that in comparing the boat speed with twin 150-HP engines, we have two reports of top speed at about 47-MPH, one from ACSEATSRI and a second from JEFF. But the boats are different, as ACSEATSRI's boat has no Whaler Drive while JEFF's boat does.

Perhaps we'll see a higher top speed from ACSEATSRI when he gets out in calmer conditions. I would expect the Whaler Drive boat to be slower because it is longer, heavier, and has more wetted surface from the Whaler Drive.

Jeff posted 05-16-2015 11:50 PM ET (US)     Profile for Jeff  Send Email to Jeff     
Jim, when on plane the entire salt shaker marine Whaler Dive bracket is running free of the water.

Jeff posted 05-17-2015 09:47 AM ET (US)     Profile for Jeff  Send Email to Jeff     
Jim,

Here is a discussion on how the Whaler Drive on this model runs while on plane. See the comments starting around 8/20 for video I shot showing it running free of the water.

http://continuouswave.com/ubb/Forum4/HTML/007721.html


Here is a video of our 23 WALKAROUND Whaler Drive running at WOT..
http://youtu.be/JrfooU6zeXU

acseatsri posted 05-18-2015 08:45 AM ET (US)     Profile for acseatsri  Send Email to acseatsri     
Had better seas and a longer run yesterday. Averaged 48.3 in both directions with about 100 lbs. more weight, probably insignificant as far as weight goes. Also keep in mind that Jeff's boat has no bottom paint, which would give him a small advantage in reduced drag.

As far as driveability and ride, the old throttle and shift cables are stretched and stiff. It's hard to keep the engines synced and control speed. I was able to run at 15 mph in heavy fog without much trouble. A modern single engine would be much easier to set a speed and hold it on plane. The boat seems to run best at around 30 mph, the engines are loafing at 3500 rpm.

Per the previous poster, I'm setting it up identically, single 250 with a kicker. The weight on the transom will only be 50 lbs lighter. The boat doesn't seem stern heavy with 780 lbs of engines.

I ran it all day yesterday with the plugs out of the fish wells. They have about 2-3 inches of water at rest and empty out quickly at above 10 mph. Jeff's boat must have the clamshells removed or crushed by the trailer bunks to have filled with water when underway.

Jeff posted 05-18-2015 12:02 PM ET (US)     Profile for Jeff  Send Email to Jeff     
A smooth hull has more drag than a rough one...

Also, we have a rather large custom Hard Top Structure compared to what was offered from the Factory...
http://img.photobucket.com/albums/v427/jeff_rohlfing/ 1993%2023%20Boston%20Whaler%20Walkaround%20Whalerdrive/ 23walkaround_82013_selects-6_zps240044e8.jpg

jimh posted 05-21-2015 09:57 PM ET (US)     Profile for jimh  Send Email to jimh     
Having spent a lot of time cruising with other Boston Whaler owners with 23 WALKAROUND boats with Whaler Drives, I have heard a lot of complaints about my choice of cruising speeds at 26-MPH. These guys with 23 WALKAROUND Whaler Drive boats always want to cruise faster, around 29-MPH. The hull of the 23 WALKAROUND seems like it wants to run on plane with good efficiency only when the boat speed is around 30-MPH, just as ACSEATSRI has observed.

Jeff--I never let those guys with 23 WALKAROUNDS get ahead of me, and therefore I don't know if their Whaler Drives are running free of the water. Maybe at the 27-MPH speed they are not quite yet out of the water. Those guys tend to follow me because I usually know where I am going, and experience has shown they all run into rocks when they are in the lead.

acseatsri posted 05-22-2015 05:52 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
The [preference for a speed of] 30-MPH at cruise may be more related to old two-smoke technology rather than the hull itself. I think lower than 30-MPH and the engines are out of their sweet spot RPM, and the boat tends to fall off plane due to the low RPM. At 25-MPH [on my boat the engines are] barely cracking 3000-RPM, especially running 19-pitch propellers. I hope in in two to four weeks I'll be able to confirm this with the single Honda 250 on the transom.
jimh posted 05-23-2015 01:11 AM ET (US)     Profile for jimh  Send Email to jimh     
The ability of any hull to operate at a particular speed is always a function of the power--specifically the torque--available from the engine to turn the propeller at the rate that produces the particular hull speed. Often at lower planing speeds the load on the engine is very high, requiring the engine to be capable of producing a lot of torque to turn the propeller at that engine speed. Some engines cannot produce the total power--torque at RPM--needed to maintain the propeller shaft speed necessary to keep the boat on plane at lower speeds.

The hull plays a big part in that determination, too, as the hull form determines when it will generate enough lift to push the hull out of the water and get onto an efficient plane.

With my classic Boston Whaler 22-foot hull form, a speed of 27-MPH is a very nice planing speed that is also very fuel efficient. The reason it is fuel efficient is that the hull does not need any extra horsepower to maintain plane. It is going fast enough so the hull form generates lift.

Peter posted 05-25-2015 07:44 AM ET (US)     Profile for Peter  Send Email to Peter     
Another factor to maintaining on-plane speed is propeller "grip". It was difficult to maintain my former Whaler 27 WD with a pair of Evinrude 225s on a slow plane (below 26 MPH) when the motors were equipped with 3 blade propellers. When the motors were equipped with 4 blade propellers, on-plane could be maintained down to 16 MPH.
acseatsri posted 05-31-2015 08:00 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
Preliminary results:
The Honda 250 is mounted in place of the twin 1993 Johnson 150 stink pots. The boat lost about 150 lbs on the transom and the batteries were moved from the side cabinets in the stern to underneath the passenger seat about 6 feet farther forward. The boat floats about 2" higher in the stern. I was surprised how much difference this small change made. I'm still sorting out the electrical system going from 2 individual systems to a single 2 battery system. Currently neither fore or aft bilge pumps are working- whether I pulled a wire or missed a connector remains to be seen. Hence a very short first run.

Spinning an older 15.25 x 17 pitch slightly dinged stainless prop of unknown manufacturer that came off a blown 300 Yamaha hpdi , the boat hit 42.3 mph at 6150 rpm with an unknown tidal current. This was with 3/4 tank of fuel and 400 lbs of passengers. Best cruise speed is 28 mph at 3.4 miles per gallon. I don't trust the Lowrance software on this count, think it's almost 20 percent too high. The prop looks like a Tempest and is not an "elephant ear" prop. I think a Rebel 15.5 x 17 or an Enertia ECO 16 x 17 prop would do a lot better.

The engine is mounted 1 hole up and could probably be raised at least 1 hole, maybe 2. The engine throws a rather large rooster tail. I started at this height because this hull seems to like to be trimmed out without much porpoising.

For the prop Gods- how much rpm would I lose going to a 19 pitch prop?

boatdryver posted 06-01-2015 10:31 AM ET (US)     Profile for boatdryver  Send Email to boatdryver     
The first thing the prop experts will ask is the brand and model of the 15.25 X 17 inch Stainless prop you were running when you obtained the data in your post.

Often just the number imprinted on the prop of unknown origin will identify it.

The rules of thumb governing rpm change from one pitch to another go out the window when one changes from one propellor design to another.

JimL

jimh posted 06-01-2015 11:09 AM ET (US)     Profile for jimh  Send Email to jimh     
You do not need a "prop god" to make an estimate of the change in engine speed that will result from an increase in propeller pitch of 2-inches. David Gerr, a naval architect who writes very understandable books about boat design, says, in his Rule of Thumb:

quote:
Every two-inch increase in propeller pitch will decrease engine speed by 450-RPM, and vice versa.

See http://continuouswave.com/ubb/Forum4/HTML/003906.html for actual tests that tend to confirm the Rule of Thumb.

jimh posted 06-01-2015 11:48 AM ET (US)     Profile for jimh  Send Email to jimh     
A boat speed of over 42-MPH with a "slightly dinged" stainless steel propeller sounds like a good outcome for the first iteration of propeller testing with the new Honda 250-HP engine.
Tom W Clark posted 06-01-2015 01:19 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Bill -- Jim L is correct, we should know what propeller you are using now to help you figure out what might work best.

Be very careful with any rule of thumb about RPM and pitch; they often do not work very well because different motors use different gear ratios, have different WOT engine speed ranges and use use different propeller pitches, all of which will affect how much the engine speed with change with a two inch change or pitch. It is much better to use jimh's excellent Propeller Calculator, which takes all of this into account by doing all the simple, but tedious, arithmetic of calculating the relationship between boat speed, engine seed, gear ratio, propeller slip and pitch.

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

For example on your boat, if you increase pitch from 17" to 19" using the same model of propeller, the engine speed will decrease, ceteris paribus, about 650 RPM. That does not comport with the rule of thumb presented above.

Likewise, one must be mindful that changing two inches of pitch will have a far greater impact on engine speed for low pitch propellers than for higher pitch propellers. This is simply because two inches is a larger percentage change for low pitch propellers and a smaller percentage change for higher pitch propellers.

For example, changing from a 13" pitch to a 15" pitch propeller on an outboard on a small boat with a 2.33:1 gear ratio will likely result in a change in engine speed of 800 RPM. The rule of thumb that every two inch increase in propeller pitch will decrease engine speed by 450 RPM is not very helpful in this example, nor for your Whaler 23 Walkaround with its Honda BF250

Tom W Clark posted 06-01-2015 01:29 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The Honda BF250 should never have been mounted only one hole up on the transom of the 23 Walkaround. Even 20 years ago when propeller design was less advanced the factory wadvised mounting the motor two holes up and I think today, with a modern prop, the motor can be three holes up.

I recommend you try a Mercury MIRAGEplus, Mercury Enertia, or Mercury Revolution4. 250 HP is a lot of power to transmit through a single propeller and you will want one with a fair amount of blade area.

I have no personal experience with the Enertia ECO, but if you had the opportunity to try one that might be a useful experiment as well.

The PowerTech! OFS4 is another good choice from a different manufacturer. Honda offers it in their own propeller catalog (Honda does [not] manufacture any of their own props, they buy them from other manufacturers, principally Solas, Precision Propeller Industries and PowerTech!).

acseatsri posted 06-11-2015 07:11 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
Tom,
The markings on the 17 pitch prop are a 17m cast into it and the Roman numeral II in another area. It is a 15.25 x 17. I'd like to drop the max rpm about 3-400. I'm most interested in economy and range for offshore runs.
Tom W Clark posted 06-12-2015 10:36 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
It is almost certainly a Yamaha Saltwater Series II. The size is 15-1/2" x 17"

If cruise speed fuel economy is your goal, try a Mercury MIRAGEplus

Tom W Clark posted 06-12-2015 10:38 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
If you combine the new propeller with raising the motor on the transom, you could probably make good use of a 15-1/4" x 19" M+ [MIRAGEplus]
acseatsri posted 06-13-2015 08:56 AM ET (US)     Profile for acseatsri  Send Email to acseatsri     
I tried an Apollo 15 1/4 x 19 pitch today. Managed 5650 rpm at 42 mph- pretty identical speed with the Yamaha prop at 500 rpm lower with 1/2 tank fuel and 3 people. Fuel economy seemed about the same, right around 2.8-3.2 mpg at any speed between 16 and 30 mph. This propeller seems like it may be better for general cruising as the engine turns about 200 to 300-RPM slower at any given [boat] speed.
jimh posted 06-13-2015 01:16 PM ET (US)     Profile for jimh  Send Email to jimh     
I have been using a Mercury MIRAGEplus propeller since c.2009 on my boat with a single 225-HP engine. It has been a very good propeller for my application. I had tried it earlier with a different engine, and I didn't think it was too good in rough seas, when it seemed to blow out or ventilate, but on the engine I have now, whose gear case is a different design, it has not shown any tendency to lose grip. I think you have to evaluate a propeller on a particular engine and particular gear case.

The gear case on a Honda BF250 might have some Mercury heritage. I believe at one time Honda was using Mercury gear cases with their engines. I don't know for certain that a new BF250 Honda has a gear case that resembles a Mercury. Assuming it did, then a Mercury propeller like a MIRAGEplus should work well with that gear case.

It is worth mentioning the recent trend seen in propeller design for specific engines. Evinrude developed their RX4 propeller specifically for their E-TEC 74-degree V6 engines and their new gear case design. Mercury developed their ENERTIA ECO specifically for their VERADO third generation engines with their third and fourth generation gear cases. These examples seem to affirm my notion that the performance of the propeller will be influenced by the gear case. That is a very reasonable assertion, if you consider that the water reaching the propeller has to flow over the gear case. It would be hard to make a case that the shape and design of the gear case would not have any effect. It must alter the water flow into the propeller.

acseatsri posted 08-23-2015 02:44 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
After running the boat for almost two months, I've decided it definitely need a different propeller. When running in heavy following seas offshore, the boat comes on and off plane and speed varies between 12 and 20-MPH without any throttle intervention when running the Apollo 19P propeller. I'm looking for better speed control and probably more stern lift to aid in keeping the bow down and on plane. If the Yamaha SWS II 17P turns 6,100 to 6,200-RPM and the Apollo 19P turns 5,500 to 5,600-RPM, I'm thinking of a Powertech OFS4 15 1/4" x 17P will probably turn around 200-RPM less than the SWS II 17p and will probably be better for heading offshore with a full load of fuel and ice, and with the additional blade area will probably regulate speed and planing better.

Opinions?

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