Forum: WHALER
  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  Crouch's Calculator

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Crouch's Calculator
jimh posted 04-23-2006 11:17 PM ET (US)   Profile for jimh   Send Email to jimh  
At the urging of Tom W. Clark, and with the assistance of my son the computer scientist, I am pleased to announce a new calculator, the Crouch's Calculator for estimating the speed potential of a planing hull based on weight, horsepower, and hull factor:

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

This calculator is implemented in the same manner as our famous PROPELLER CALCULATOR, which permits any of the values to be calculated from the other operators.

By using these two calculators in concert, you can make useful predictions about a number of values related to your boat's performance.

Perry posted 04-23-2006 11:57 PM ET (US)     Profile for Perry  Send Email to Perry     
Wow, using the existing 180 hull factor, the speed of my boat (190 Outrage w/135 HP) was within 2 tenths of actual top speed measured by gps.
jimh posted 04-24-2006 10:59 AM ET (US)     Profile for jimh  Send Email to jimh     
The calculator is useful for deducing the hull factor from actual observations for weight, horsepower, and speed. In this case, it sound like the hull factor for a 190 NANTUCKET is about 180. Perhaps we can accumulate more data about Whaler hull factors by using the calculator to deduce them from test data.
Tom W Clark posted 04-24-2006 11:08 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Jim,

Thank you (and JFH) for this handy tool. I am still curious about the potential accuracy of Crouch's formula and look forward to other's reported calculations of their hull factors.

One of the fun things you can do with the "Crouch Calc." is estimate how much actual horsepower it takes to propel your boat at a given boat speed.

rtk posted 04-24-2006 11:10 AM ET (US)     Profile for rtk  Send Email to rtk     
1997 21 Outrage data.

Total weight: +/- 4400lbs (full fuel)
250 horsepower
Top speed 48 miles per hour

Calculates a hull factor of 201.44

Very nice tool.

Rich

hauptjm posted 04-24-2006 11:48 AM ET (US)     Profile for hauptjm    
1985 18ft. Outrage with solid transom with a 1995 150 hp Johnson Oceanrunner on an Armstrong Bracket using an operating weight of 2000 lbs. and observed speed of 52 m.p.h. delivered a hull constant of 189.9. Seems pretty accurate.
Peter posted 04-24-2006 01:04 PM ET (US)     Profile for Peter  Send Email to Peter     
I'm surprised by the 180 hull constant for the 190 Outrage. If you plug all of the Whaler performance report data into the calculator and and let the calculator solve for the hull constant, the calculator shows the hull constant to be in the range of 205 to 210.

Plotman posted 04-24-2006 02:02 PM ET (US)     Profile for Plotman  Send Email to Plotman     
Very interesting. When I solve for the hull factor of my 22 outrage, I get 182 (using a weight that takes into account fuel, engines, etc.) Now maybe there needs to be an adjustment for twin engines vs a single, but I find it odd that the 190 outrage, which allegedly weighs the same as a classic 22 outrage, has a hull factor that much higher.

However, when I input my performance observations of how my boat does on a single engine, I get a hull factor of 200.

David

Peter posted 04-24-2006 02:12 PM ET (US)     Profile for Peter  Send Email to Peter     
If you compare the hull shape of 190 Outrage to the classic 18 Outrage, you'll notice a very big, nearly flat pad (very little "deadrise") in the stern most 1/4 of the hull on the 190 Outrage. It doesn't carry the vee to the transom like the classic 18 Outrage does. My recollection is that the lifting strakes on the 190 carry all the way to the transom as well. Accordingly, that flatish pad area and the lifting strakes will increase the hull factor.
Bulldog posted 04-24-2006 03:03 PM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Did the calculations on my 20' Revenge with twin 70hp engines, top speed is 35.5 MPH that is right on, formula works pretty neat...Jack
Bulldog posted 04-24-2006 03:13 PM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Couple neat things , taking my same 20' Revenge that total weight is about 3600lbs. and pulling off the twin 70 hp Yamahas (226lbs each) and going with twin 75hp E-techs (326 lbs each) I get around 35.8 MPH and if I go with the 90hp E-techs with no more weight then the 75 engines I'm at a top speed of 39.2 MPH, not much improvement for me, I did figure on adding two hundred pounds to boat weight because of the heavier engines.......Jack
Perry posted 04-24-2006 05:04 PM ET (US)     Profile for Perry  Send Email to Perry     
Peter, I ran the numbers again today for my 190 Outrage/Nantucket and it appears I input the wrong weight for my boat. I must have entered 2000 lbs by accident instead of the 3000 lbs that I estimate my boat weighs when top speed of 46 mph (gps) is measured.

Using 3000 lbs as the weight weight, 135 HP and 46 mph, Crouch's Calculator gives a hull factor of over 216. I ran the numbers published by Boston Whaler's performance data for the 190 Outrage with 4 different motors and the hull factor ranges from 205 to 211.

Either my boat is way lighter than most 190's or my Honda BF135 puts out more power than 135 HP.

Perry posted 04-24-2006 05:23 PM ET (US)     Profile for Perry  Send Email to Perry     
Oh, and the lifting strakes do carry all the way to the transom. Here is a picture of the stern of a 190 Nantucket from Cetacea page 71 on Continuous Wave:

http://img.photobucket.com/albums/v235/perrycl/ 19-NantucketTransom640x510.jpg

Peter posted 04-24-2006 05:46 PM ET (US)     Profile for Peter  Send Email to Peter     
Perry -- I had a feeling that there might be an incorrect weight in the calculation or that you were not counting all the weight.

There could be many reasons why the hull factor number comes out higher or lower than an average in a given case, including unaccounted for actual weight differences, motor mounting height, motor trim, propeller efficiency, actual versus nominal HP variations and actual hull shape variations. No two hulls will be exactly alike no matter how good the manufacturing process is so the actual hull factor from boat to boat is going to vary a bit for any given model. If we collect enough performance data for a particular hull, we should be able to get a pretty good determination of the average hull factor which will ordinarly be good enough for prediction purposes.

deepwater posted 04-24-2006 06:11 PM ET (US)     Profile for deepwater  Send Email to deepwater     
holy sh***,,i just wag'ed in my weight and it hit with in .5 of what I'm doing now
hardknots posted 04-25-2006 02:11 PM ET (US)     Profile for hardknots  Send Email to hardknots     
Jimh:
This tool is great. My boat is within 3/4 to 1 mile faster, maybe it weights a bit less than the 5000 lb I'm using. But hey this thing really works. Collecting this data will help all of us when the time comes to repower.

25' Classic Outrage w/ twin 2 stroke V4 Yamaha 130's
Weight +/- 5000 lb.
HP 260
Hull factor 180
Speed 41 mph (Actual max speed by gps is 42 mph)

Congrats to you and your son for another great tool on Continuous wave.

Ricky

TC posted 04-25-2006 06:10 PM ET (US)     Profile for TC  Send Email to TC     
With my 18' Guardian figured at 1700 pounds, it shows around 53 MPH with a 150 HP, and about 62 MPH with a 200. Do these numbers seem accurate to you all? I just bought an old used 200 since the 150 was shot.
Tom W Clark posted 04-25-2006 06:18 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
TC,

Your speed figures are high because your weight figures are way too low.

An 18' Guardian is 1750 pounds. A 150 HP two stroke outboard is 400 pounds. One single group 24 battery is 45 pounds. A full tank of fuel is another 400 pounds. Extras gear and options? How much do you weigh? Add it all up and run the calculation again. I think you will see more realistic output.

Peter posted 04-25-2006 06:21 PM ET (US)     Profile for Peter  Send Email to Peter     
No. You need to add the weight of: motor (450 lbs), fuel (400 lbs), gear (150 lbs) and people (200 lbs). Total weight for the Guardian will be in the neighborhood of 2900 lbs. Plugging that into the calculator will yield 40.9 MPH with a 150 HP motor and 47.9 MPH with a 200.
TC posted 04-25-2006 06:33 PM ET (US)     Profile for TC  Send Email to TC     
D'OH! Thanks for the reality check.
JMARTIN posted 04-25-2006 07:04 PM ET (US)     Profile for JMARTIN  Send Email to JMARTIN     
What is also pretty cool is knowing what the boat will do for speed, I now have a pretty good guess of how much weight I have on board. It looks like 1850 lbs. Sounds reasonable for 2 motors, 2 guys, 70 gallons of fuel, 3 batteries, oil tank, camping on the boat gear, all the fishing gear, anchoring equipment, and all the other stuff.

Just curious, what does my 1992 200 hp Evinrude weigh in at?

John

Peter posted 04-25-2006 07:31 PM ET (US)     Profile for Peter  Send Email to Peter     
About 450 lbs.
phatwhaler posted 04-25-2006 09:23 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
1996 19/20 Outrage w T-top

Boat/Motor/Batt/Fuel/Gear 3700 lbs.
Top Speed 43mph
2.5L Mercury 150 EFI 160 HP
Hull Factor 207

Phatwhaler out.

Tom W Clark posted 04-26-2006 01:49 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
For my own Revenge 25 Walk Through with twin 150 HP motors, I calculate the following hull factor based on a set of data from an afternoon of propeller testing.

On that day I estimate the total weight to be 5700 pounds and a top speed of 47 MPH. With 300 HP that calculates the hull factor at 205. Seem high?

Here is the conundrum: If I had filled the fuel tank to its 140 gallon capacity instead of the 40 gallons I had in it at the time there would have been an extra 600-650 pounds, no?

So recalculating the potential top speed with the extra weight knowing the hull factor, the Crouch Calculator tells me it would have only gone 44.5 MPH.

I reject that estimate. I do not believe the added weight would affect the top speed that much and this is where I think Crouch's formula breaks down. I am not sure his formula is geared well towards boats with high power to weight ratios.

jimh posted 04-26-2006 05:17 PM ET (US)     Profile for jimh  Send Email to jimh     
Tom--Get the test data and see what happens. Of course, it is hard to burn off that much fuel before all the other conditions change, too.
jimh posted 04-26-2006 08:30 PM ET (US)     Profile for jimh  Send Email to jimh     
Wait--I've got it. Run the boat with light fuel, then add dead weight. Give us the numbers. Then we can see if the formula predicts the change in speed correctly.

If it gets warm enough to try this in Michigan, I will attempt to test for this myself.

Wiscbw posted 04-26-2006 11:12 PM ET (US)     Profile for Wiscbw  Send Email to Wiscbw     
1996 19 Outrage
Weight with 2 people and 1/2 tank of fuel 3450 lbs.

measured top speed 52 mph
engine 225 Yamaha EFI
Hull Factor 200

Crouch Calculator value 51 mph
That is a pretty good estimate

Tom W Clark posted 04-27-2006 11:04 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Jim,

The test for me would be, as we discussed last week, to run the boat with near empty fuel, pull the boat, drive to the gas station and fill it up, then re-launch the boat and test again. I might just do this.

The other, perhaps easier way to test would be to recruit numerous human bodies and take them for a ride after initial, low-on-fuel testing. Hmmm...I can think of several friends who might object to being weighed as they come on board....

JMARTIN posted 04-27-2006 12:36 PM ET (US)     Profile for JMARTIN  Send Email to JMARTIN     
The hull factor of 180 works very well for my 1983 Revenge 22, notched transom, 200hp, and quite a bit of gear on board. John
newt posted 04-27-2006 05:06 PM ET (US)     Profile for newt  Send Email to newt     
1980 V20 Revenge.
150 HP.
Estimated Weight = 3200 lb.
Top speed = 40 mph

Calculated hull Factor = 185

pglein posted 05-08-2006 01:48 PM ET (US)     Profile for pglein  Send Email to pglein     
This tool is really great, but I have one question? What the heck is a "mile per hour"? Is that kind of like a knot?
cbgann posted 05-08-2006 09:38 PM ET (US)     Profile for cbgann  Send Email to cbgann     
Tried the calculator for my 15' with 60hp Yamaha and 3 gal. fuel. Using 1000# weight and 180 formula gives 44mph. Using actual speed, constant comes out at 150?? Bill
Tom W Clark posted 05-08-2006 09:50 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Bill,

You probably underestimated your boat's weight. 15 foot what? Model? Year?

cbgann posted 05-08-2006 10:00 PM ET (US)     Profile for cbgann  Send Email to cbgann     
Thanks Tom, It is an 89 bare hull with a 45# casting deck and a 35#center console, starting battery ,6 gal plastic tank and the Pro 60 Yamaha. Bill
cbgann posted 05-09-2006 04:01 PM ET (US)     Profile for cbgann  Send Email to cbgann     
Sometimes it doesn't pay to think after dinner. I have a Pro 50, not a pro 60. That was good for -4mph. Resync'ing the carbs also helped now within 1+ mph of projected speed.
Thanks to Tom and Jim for a very handy tool. Bill
wireflight posted 09-02-2006 04:40 AM ET (US)     Profile for wireflight  Send Email to wireflight     
This is more of a technical question than anything related to Boston Whalers per se.

According to http://continuouswave.com/cgi-bin/crouchcalc.pl, “PLANING HULL SPEED CONSTANTS--MPH:”

C Hull Type

172 Average runabout, cruiser, passenger vessel
218 High-speed runabout, very light high-speed cruiser
240 Race boat types
253 Three-point hydroplanes, stepped hydroplanes
265 Racing power catamarans and sea sleds

I decided to use the Crouch formula to evaluate several historical military high-performance boats. Assuming 2,240 pounds per ton (English “long ton”), here’s what I found for the following MTB (motor torpedo boat) hulls:

Hull type (displacement), (Throttle: speed), Gross Horsepower, Crouch’s Constant
Kriegsmarine: S100 class (120 tons), (Full: 43.8 knots), 6000, 337.4
Kriegsmarine: S100 class (120 tons), (Flank: 48 knots), 7500, 330.7
Kriegsmarine: S130 (120 tons), (Full: 40 knots), 6000, 308.1
Kriegsmarine: S208 (120 tons), (Full: 40 knots), 6000, 308.1
Kriegsmarine: S100 class (120 tons), (Full: 43.5 knots), 7500, 299.7
PT 811 (90 tons), (Full: 55 knots), 10000, 284.2
PT 9 (40 tons), (Full: 45 knots), 3000, 283.0
Repowered: S130 (120 tons), (Full: 45 knots), 9420, 276.6
RCN: Hythe MTB (55 tons), (Full: 41 knots), 3750, 270.4
80-ft ELCO (51 tons), (Full: 43 knots), 4050, 262.8
80-ft ELCO (61 tons), (Full: 41 knots), 4500, 260.0
77-ft ELCO (46 tons), (Full: 42 knots), 3600, 258.6
70-ft ELCO (40 tons), (Full: 45 knots), 3600, 258.3
RCN: British Power Boats MTB (55 tons), (Full: 38 knots), 3750, 250.6
Type II Vosper (49 tons), (Full: 40 knots), 4200, 235.3
Type I Vosper (47 tons), (Full: 40 knots), 4200, 230.5
1943 Higgins PT (43 tons), (Full: 40 knots), 4050, 224.5
Vosper PT (47 tons), (Full: 38 knots), 4050, 223.0
PT 1 (30 tons), (Full: 30 knots), 2000, 200.1
PT 2 (30 tons), (Full: 30 knots), 2000, 200.1
PT 3 (30 tons), (Full: 32 knots), 2400, 194.9
PT 4 (30 tons), (Full: 32 knots), 2400, 194.9

Although the source documents specifically expressed the foregoing speeds in knots (and often differentiated between knots and mph), I elected to see the effect of changing the units to mph without altering the numeric value for the speed:

Hull type (displacement), (Throttle: speed), Gross Horsepower, Crouch’s Constant
Kriegsmarine: S100 class (120 tons), (Full: 43.8 mph), 6000, 293.2
Kriegsmarine: S100 class (120 tons), (Flank: 48 mph), 7500, 287.4
Kriegsmarine: S130 (120 tons), (Full: 40 mph), 6000, 267.7
Kriegsmarine: S208 (120 tons), (Full: 40 mph), 6000, 267.7
Kriegsmarine: S100 class (120 tons), (Full: 43.5 mph), 7500, 260.4
PT 811 (90 tons), (Full: 55 mph), 10000, 246.9
PT 9 (40 tons), (Full: 45 mph), 3000, 245.9
Repowered: S130 (120 tons), (Full: 45 mph), 9420, 240.4
RCN: Hythe MTB (55 tons), (Full: 41 mph), 3750, 235.0
80-ft ELCO (51 tons), (Full: 43 mph), 4050, 228.4
80-ft ELCO (61 tons), (Full: 41 mph), 4500, 225.9
77-ft ELCO (46 tons), (Full: 42 mph), 3600, 224.7
70-ft ELCO (40 tons), (Full: 45 mph), 3600, 224.5
RCN: British Power Boats MTB (55 tons), (Full: 38 mph), 3750, 217.8
Type II Vosper (49 tons), (Full: 40 mph), 4200, 204.5
Type I Vosper (47 tons), (Full: 40 mph), 4200, 200.3
1943 Higgins PT (43 tons), (Full: 40 mph), 4050, 195.1
Vosper PT (47 tons), (Full: 38 mph), 4050, 193.7
PT 1 (30 tons), (Full: 30 mph), 2000, 173.9
PT 2 (30 tons), (Full: 30 mph), 2000, 173.9
PT 3 (30 tons), (Full: 32 mph), 2400, 169.3
PT 4 (30 tons), (Full: 32 mph), 2400, 169.3

On the off chance the data was translated into tonnes before being recorded, I substituting the tonne for the long ton, which revealed the following:

Hull type (displacement), (Throttle: speed), Gross Horsepower, Crouch’s Constant
Kriegsmarine: S100 class (120 tonnes), (Full: 43.8 knots), 6000, 334.7
Kriegsmarine: S100 class (120 tonnes), (Flank: 48 knots), 7500, 328.1
Kriegsmarine: S130 (120 tonnes), (Full: 40 knots), 6000, 305.7
Kriegsmarine: S208 (120 tonnes), (Full: 40 knots), 6000, 305.7
Kriegsmarine: S100 class (120 tonnes), (Full: 43.5 knots), 7500, 297.3
PT 811 (90 tonnes), (Full: 55 knots), 10000, 281.9
PT 9 (40 tonnes), (Full: 45 knots), 3000, 280.8
Repowered: S130 (120 tonnes), (Full: 45 knots), 9420, 274.4
RCN: Hythe MTB (55 tonnes), (Full: 41 knots), 3750, 268.3
80-ft ELCO (51 tonnes), (Full: 43 knots), 4050, 260.7
80-ft ELCO (61 tonnes), (Full: 41 knots), 4500, 257.9
77-ft ELCO (46 tonnes), (Full: 42 knots), 3600, 256.5
70-ft ELCO (40 tonnes), (Full: 45 knots), 3600, 256.3
RCN: British Power Boats MTB (55 tonnes), (Full: 38 knots), 3750, 248.7
Type II Vosper (49 tonnes), (Full: 40 knots), 4200, 233.4
Type I Vosper (47 tonnes), (Full: 40 knots), 4200, 228.6
1943 Higgins PT (43 tonnes), (Full: 40 knots), 4050, 222.7
Vosper PT (47 tonnes), (Full: 38 knots), 4050, 221.2
PT 1 (30 tonnes), (Full: 30 knots), 2000, 198.5
PT 2 (30 tonnes), (Full: 30 knots), 2000, 198.5
PT 3 (30 tonnes), (Full: 32 knots), 2400, 193.3
PT 4 (30 tonnes), (Full: 32 knots), 2400, 193.3

Again changing the units to mph without altering the numeric value for the speed:

Hull type (displacement), (Throttle: speed), Gross Horsepower, Crouch’s Constant
Kriegsmarine: S100 class (120 tonnes), (Full: 43.8 mph), 6000, 290.8
Kriegsmarine: S100 class (120 tonnes), (Flank: 48 mph), 7500, 285.1
Kriegsmarine: S130 (120 tonnes), (Full: 40 mph), 6000, 265.6
Kriegsmarine: S208 (120 tonnes), (Full: 40 mph), 6000, 265.6
Kriegsmarine: S100 class (120 tonnes), (Full: 43.5 mph), 7500, 258.4
PT 811 (90 tonnes), (Full: 55 mph), 10000, 245.0
PT 9 (40 tonnes), (Full: 45 mph), 3000, 244.0
Repowered: S130 (120 tonnes), (Full: 45 mph), 9420, 238.5
RCN: Hythe MTB (55 tonnes), (Full: 41 mph), 3750, 233.1
80-ft ELCO (51 tonnes), (Full: 43 mph), 4050, 226.6
80-ft ELCO (61 tonnes), (Full: 41 mph), 4500, 224.1
77-ft ELCO (46 tonnes), (Full: 42 mph), 3600, 222.9
70-ft ELCO (40 tonnes), (Full: 45 mph), 3600, 222.7
RCN: British Power Boats MTB (55 tonnes), (Full: 38 mph), 3750, 216.1
Type II Vosper (49 tonnes), (Full: 40 mph), 4200, 202.9
Type I Vosper (47 tonnes), (Full: 40 mph), 4200, 198.7
1943 Higgins PT (43 tonnes), (Full: 40 mph), 4050, 193.5
Vosper PT (47 tonnes), (Full: 38 mph), 4050, 192.2
PT 1 (30 tonnes), (Full: 30 mph), 2000, 172.5
PT 2 (30 tonnes), (Full: 30 mph), 2000, 172.5
PT 3 (30 tonnes), (Full: 32 mph), 2400, 168.0
PT 4 (30 tonnes), (Full: 32 mph), 2400, 168.0

And finally, even though I can’t imagine that it would really be appropriate, using short tons:

Hull type (displacement), (Throttle: speed), Gross Horsepower, Crouch’s Constant
Kriegsmarine: S100 class (120 tons), (Full: 43.8 knots), 6000, 318.8
Kriegsmarine: S100 class (120 tons), (Flank: 48 knots), 7500, 312.5
Kriegsmarine: S130 (120 tons), (Full: 40 knots), 6000, 291.1
Kriegsmarine: S208 (120 tons), (Full: 40 knots), 6000, 291.1
Kriegsmarine: S100 class (120 tons), (Full: 43.5 knots), 7500, 283.2
PT 811 (90 tons), (Full: 55 knots), 10000, 268.5
PT 9 (40 tons), (Full: 45 knots), 3000, 267.4
Repowered: S130 (120 tons), (Full: 45 knots), 9420, 261.4
RCN: Hythe MTB (55 tons), (Full: 41 knots), 3750, 255.5
80-ft ELCO (51 tons), (Full: 43 knots), 4050, 248.3
80-ft ELCO (61 tons), (Full: 41 knots), 4500, 245.7
77-ft ELCO (46 tons), (Full: 42 knots), 3600, 244.3
70-ft ELCO (40 tons), (Full: 45 knots), 3600, 244.1
RCN: British Power Boats MTB (55 tons), (Full: 38 knots), 3750, 236.8
Type II Vosper (49 tons), (Full: 40 knots), 4200, 222.4
Type I Vosper (47 tons), (Full: 40 knots), 4200, 217.8
1943 Higgins PT (43 tons), (Full: 40 knots), 4050, 212.1
Vosper PT (47 tons), (Full: 38 knots), 4050, 210.7
PT 1 (30 tons), (Full: 30 knots), 2000, 189.1
PT 2 (30 tons), (Full: 30 knots), 2000, 189.1
PT 3 (30 tons), (Full: 32 knots), 2400, 184.1
PT 4 (30 tons), (Full: 32 knots), 2400, 184.1

Again changing the units to mph without altering the numeric value for the speed:

Hull type (displacement), (Throttle: speed), Gross Horsepower, Crouch’s Constant
Kriegsmarine: S100 class (120 tons), (Full: 43.8 mph), 6000, 277.0
Kriegsmarine: S100 class (120 tons), (Flank: 48 mph), 7500, 271.5
Kriegsmarine: S130 (120 tons), (Full: 40 mph), 6000, 253.0
Kriegsmarine: S208 (120 tons), (Full: 40 mph), 6000, 253.0
Kriegsmarine: S100 class (120 tons), (Full: 43.5 mph), 7500, 246.1
PT 811 (90 tons), (Full: 55 mph), 10000, 233.3
PT 9 (40 tons), (Full: 45 mph), 3000, 232.4
Repowered: S130 (120 tons), (Full: 45 mph), 9420, 227.1
RCN: Hythe MTB (55 tons), (Full: 41 mph), 3750, 222.1
80-ft ELCO (51 tons), (Full: 43 mph), 4050, 215.8
80-ft ELCO (61 tons), (Full: 41 mph), 4500, 213.5
77-ft ELCO (46 tons), (Full: 42 mph), 3600, 212.3
70-ft ELCO (40 tons), (Full: 45 mph), 3600, 212.1
RCN: British Power Boats MTB (55 tons), (Full: 38 mph), 3750, 205.8
Type II Vosper (49 tons), (Full: 40 mph), 4200, 193.2
Type I Vosper (47 tons), (Full: 40 mph), 4200, 189.2
1943 Higgins PT (43 tons), (Full: 40 mph), 4050, 184.3
Vosper PT (47 tons), (Full: 38 mph), 4050, 183.1
PT 1 (30 tons), (Full: 30 mph), 2000, 164.3
PT 2 (30 tons), (Full: 30 mph), 2000, 164.3
PT 3 (30 tons), (Full: 32 mph), 2400, 160.0
PT 4 (30 tons), (Full: 32 mph), 2400, 160.0

With numbers being so high for these vessels, which obviously weren’t catamarans, I’m wondering if (a) the formula is accurate, and (b) if the generalizations are genuinely representative. Especially since published figures for military vehicle performance tends to understate potential (often by a wide margin), it is conceivable that the actual constants could be significantly higher.

Or have I badly misunderstood some important thing?

I’m a novice, so for those that know better, none of this is intended to be inflammatory: I’m just trying to learn. I welcome constructive correction.

jimh posted 09-07-2006 01:28 PM ET (US)     Profile for jimh  Send Email to jimh     
Crouch's forumula is based on the hull weight. Sometimes figures given in tonnes are really more of a rating of the hull's size or capacity, rather than an actual weight. This could be a factor.

Also, Crouch's forumula was probably intended for more moderate speed vessels. But thanks for the interesting numbers!

Sturgeon posted 12-08-2006 09:42 AM ET (US)     Profile for Sturgeon  Send Email to Sturgeon     
How does the formula apply to low-horesepower calculations? For example I am considering re-powering a 20-foot salt water boat with only a 25-HP because I only fish the sea lanes in Tampa Bay. I am never more that two miles from shore so speed to get back in is not a [concern]. I am really interested in the gas mileage to do some long distance cruising in the ICW. Not the usual application I know, but everyone is different. Thanks for any input.
jimh posted 12-08-2006 09:46 AM ET (US)     Profile for jimh  Send Email to jimh     
From the instructions for use of Crouch's Calculator:

"This calculator is based on a formula developed by Naval Architect George Crouch who showed that a useful estimate of the speed of a moderate planing hull could be derived from the boat's weight, horsepower, and hull factor."

The calculator does not attempt to predict speeds when the hull is in displacement mode.

Bayman posted 08-07-2007 04:09 PM ET (US)     Profile for Bayman  Send Email to Bayman     
I used your calculator to give me calculated speed for my old cruiser w/260 hp inboard. I Used 6900# weight (fuel and crew) and basic hullform 172 and get 33.4 mph. The old tub runs about 28@3800 which is a s hard as I care to push it. Is my hull form really down to 144.2 clean bottom (trailered boat). Is there an adjustment for inboard/sterndrive? Is there a conversion factor for diesel sterndrive since I'm leaning that way?
Thanks.
jimh posted 08-07-2007 05:53 PM ET (US)     Profile for jimh  Send Email to jimh     
Use the companion PROPELLER CALCULATOR to see how effectively your propeller is working:

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

Also, your engine is probably rated at the drive shaft, and horsepower at the propeller may be lower.

Plotman posted 08-08-2007 10:02 AM ET (US)     Profile for Plotman  Send Email to Plotman     
Remember the formula calculates speed based on the actual horsepower being supplied to the prop.

An inboard is rated at the driveshaft - you have lower unit losses you have to take into account. Also, the 3800 rpm that is the upper end you want to run at sounds like it isn't the WOT that would give you the 260hp your engine is rated at.

Stevebaz posted 08-08-2007 08:04 PM ET (US)     Profile for Stevebaz  Send Email to Stevebaz     
works very well for us little whalers (11 footer)once you actually add up all the lard my boat carries, within .5 mph from actual, measured by gps. Probably dead on with dead flat water. now to figure out how to get the lard out do you have a calculator for that?
Thank You for putting this formula together.
steve

Post New Topic  Post Reply
Hop to:


Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.