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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

Motoring speed

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kevinmac
Admiral

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USA
732 Posts

Initially Posted - 02/05/2006 : 09:10:51

If you have a knotmeter on your C250, would you mind posting here a short message that indicates the type and horsepower of your outboard, and how fast your boat goes through the water (not GPS speed) when you are at full throttle?

Last week, I got about 4 1/2 to 5 knots with near full power on my Yamaha 8 HP outboard, I am wondering if that is what I should expect. I thought hull speed on the C250 would be a little higher. I am also wondering if my knotmeter is calibrated correctly. I have not done a times run over a defined distance yet.

Thanks.

Kevin Mackenzie
Former Association Secretary and Commodore
"Dogs Allowed"
'06 C250WK #881
and
"Jasmine"
'01 Maine Cat 30 #34

Edited by - on

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 02/05/2006 : 09:27:20

Tohatsu 9.8 (2005)
We got 5+ knots by the st40 but not at full throttle (haven't been there yet.)

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frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 02/05/2006 : 09:29:21

With our Tohastu 9.8 we will usually run a little over 5 knots at between 1/2 and 3/4 throttle in smooth water. The ruffer the water and the more tide movement the more throttle to make 5 knots which is the travel speed we use when cruise planning. We have not found the need to run at full throttle yet other than during the breakin period. Usually 3/4 throttle is about as high as we go to maintain the 5 knot figure and that is in some beat you up water and winds.

Edited by - frog0911 on 02/05/2006 09:32:50

Bay Tripper
1st Mate

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USA
56 Posts

Response Posted - 02/05/2006 : 09:56:12

My Yamaha 9.9 long shaft gives me 5+ knots with 1/2 throttle. I have tried to go to full throttle and get to much agitation to the rudder.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/05/2006 : 10:52:33

Kevin,

Although I have a C25, the principles should relate to your boat.

A few years ago, I experimented with a high thrust prop (lower pitch/larger diameter), but the result was a lower top end speed at full throttle. Putting the original prop back on gave me a higher top speed somewhere between 1/2 and 3/4 throttle.

Additionally, with my prop set up, as I mentioned earlier I achieve top speed somewhere around 1/2 to 3/4 throttle. If I try to go full throttle, the bow lifts, the stern squats, and the motor labors, which results in the boat slowing down considerably. If I back off the throttle, the boat picks up speed.

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 02/05/2006 : 12:57:51

When I first started cruising my c250 wb... I used a Honda 8 Classic long shaft, and had no problems cruising at 6.5 mph at about half throttle. It would reach 7.3 mph (6.3 knots) at 3/4 throttle and above 3/4 throttle the boat would slow as outlined by Don, because of increased drag caused by turbulence of the prop. Interestingly, I don't notice a drop in speed when using the newer high thrust motor, probably because the boat never reaches full hull speed running into the obstacle that creates huge amounts of drag for a prop when it can't gain bite because the hull is held back from increased speed.

After I switched to the Honda 8 high thrust (post 2001 motor) with extra long shaft, cruising speeds dropped about 3-5 mph to 6.2-6.0 mph (5.4-5.2 knots). Very interesting and seemingly the question here, the high thrust motor struggles very hard to reach full hull speed, where the Classic 8 did so without any serious struggle. I believe the differerance is in the design of the props.

The Classic 8 had a three blade higher pitch prop compared to a 4 very large blades on the high thrust version with less pitch. The high thrust prop in my opinion simply has more drag to overcome. I should make note of the shaft differance of 5 inches which would have to add more drag.

Quite frankly, I'm disapointed by the high thrust version in that the performance loss also is very obvious in the fuel economy difference.
Note: keep in mind, I use mph because charts for the Great Lakes are in statue miles rather than nautical. Adjusting, multiply mph x .87 = knots.

Edited by - Arlyn Stewart on 02/05/2006 13:01:19

frankr
Captain

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256 Posts

Response Posted - 02/05/2006 : 15:40:01

Same here about 5 Kts at 1/2 throttle with a 9.9 Tohatsu. Usually I run at 4.5 kts which seems to give about 1/3 gallon an hour comsumption.

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kevinmac
Admiral

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USA
732 Posts

Response Posted - 02/06/2006 : 08:47:11

So what is the advantage to a "high thrust" prop if the boat is slower? Sorry, motors are a new thing to me.

Do you think a prop change on my Yamaha 8HP XLS "High Thrust" motor would get me higher speed?

Thanks.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/06/2006 : 16:49:58

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by kevinmac
 So what is the advantage to a "high thrust" prop if the boat is slower?<hr height="1" noshade id="quote"></blockquote id="quote">

So you can powerload the boat onto the trailer!

But seriously, those who use power around the docks claim the high thrust motors/props aid in manueverability.

Because I use little to no motor around our rather tight docks, having a high thrust motor is not of much use to me.

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aeckhart
Master Marine Consultant

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USA
1709 Posts

Response Posted - 02/06/2006 : 19:19:01

Horse power and prop thrust are necessary for more than just speed. In our sailing area - Lake Superior, when the wind picks up and the waves get big, and you need to use your motor to plow through both,you need one, the other, or a good combination of both. The recently popular high thrust prop on 8 hp motors provides adquate push/thrust and fuel economy in moderate conditions. As Arlyn points out though, the trade off is speed. I for one don't motor more than 5 to 5 1/2 knots and I'm not sure my 9.9 2-stroke Evinrude will push my C25 much past 6 1/2 knots. I want plenty of thrust or power to punch through wind and wave when I need to, so when I repower,I will opt for another 10 hp motor, but with the fuel economy of a 4-stroke.

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