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 Catalina/Capri 25/250 Sailor's Forums
 Catalina 25 Specific Forum
 High Thrust prop		  New Topic  Topic Locked
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sailboat
Navigator

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USA
149 Posts
Initially Posted - 11/19/2015 :  16:16:48  Show Profile
We have a 9.9 two stroke with a three blade prop on Chariots of Fire that runs like a Swiss watch. The boat will cruise at almost 6kts (GPS no current)which is terrific. However, when towing the newly acquired 9' inflatable the drag is significant and 1kt is lost. Would the addition of a High Thrust (I think they are four bladed) prop get that knot back?

Thanks,
Mike
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version

DavidBuoy
Admiral

Members Avatar

USA
707 Posts
Response Posted - 11/19/2015 :  17:28:24  Show Profile
I couldn't really tell a difference when I put my high thrust prop on. A bit better grab for initial shove off but not really a difference on the top end. I have a Tohatsu 6hp.

Captain Rob & Admiral Alyson
"David Buoy"-1985 C25 SK/SR #5053
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WesAllen
Navigator

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USA
222 Posts
Response Posted - 11/19/2015 :  19:49:10  Show Profile
I had a 3 blade on my 9.9 Merc. It was suppose to have a 4 blade. I put it on (expensive) and notice no difference in speed. It does start and stop the boat better. I notice no difference when pulling my inflatable.
Wesley Allen
"Breaking Wind"
1982 C-25 SR/TR/SK #2773
Hemlock, MI
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Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts
Response Posted - 11/19/2015 :  21:23:05  Show Profile
You'll need more RPMs to maintain a given speed, but the dinghy will probably not affect your top speed quite as much. It'll be like driving up a hill in 4th gear instead of 5th.

However, I never tried to cruise at 6 knts--too much noise and fuel that close to hull speed, where the transom started to drag. I kept it to 5.5 or below, for a lot less effort from the outboard.

I agree that the primary advantage of a larger, lower pitch prop is starting, stopping, and maneuvering around the dock. My high-thrust Honda 8 could stop my C-25 as if it had run into a pillow. At speed, the standard prop might be very slightly more efficient--until you add some drag (as you found).

Also, are you leaving an outboard on the dinghy? That'll add to its drag somewhat.
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
Edited by - Stinkpotter on 11/19/2015 21:29:11
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sailboat
Navigator

Members Avatar

USA
149 Posts
Response Posted - 11/19/2015 :  21:56:24  Show Profile
No motor on the dinghy. Currents are a real challenge in Puget Sound, which is why all trips are planned to take full advantage of them. We do run at about 5.8 so slowing to 5 is a big percentage loss hence the search to get some of that back.

Thanks,
Mike
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version
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DavidBuoy
Admiral

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USA
707 Posts
Response Posted - 11/20/2015 :  05:41:26  Show Profile
To be honest, I think my prop was $70? Yours may be different, but you can always give it a shot. "Actual User Experience May Differ".

Captain Rob & Admiral Alyson
"David Buoy"-1985 C25 SK/SR #5053
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sailboat
Navigator

Members Avatar

USA
149 Posts
Response Posted - 11/20/2015 :  12:29:52  Show Profile
The local outboard shop wants $115 for the Mercury high thrust prop. Will shop around. Thanks.
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version
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awetmore
Master Marine Consultant

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USA
1144 Posts
Response Posted - 11/20/2015 :  14:22:16  Show Profile
Why not deflate and pack the dinghy? It's safest when trying to cover real distances (like crossing the straits) and gives you the best performance as well.

I've found different dinghies to have different amounts of drag too.
Alex W
Seattle, WA
Express 37 "re-Quest"
previously owned 1984 Catalina 25 "Lutra"
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sailboat
Navigator

Members Avatar

USA
149 Posts
Response Posted - 11/21/2015 :  00:07:29  Show Profile
Packing is an option but sailing when the weather is cold I like having the option of being able to jump into it if necessary. I will experiment with different towing distances.
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version
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Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts
Response Posted - 11/21/2015 :  08:35:19  Show Profile
If you are running at a speed that generates stern waves (which generally only occurs close to hull speed where the boat starts to squat), you want to adjust the painter so the dinghy is running on the front side of one of the waves so it can surf a little. Otherwise, the theoretical hull speed of the dinghy is under 4 kts, so it will nose up and create drag.
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
Edited by - Stinkpotter on 11/21/2015 08:36:37
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sailboat
Navigator

Members Avatar

USA
149 Posts
Response Posted - 11/21/2015 :  11:39:21  Show Profile
Thanks, I will experiment with towing distance prior to purchasing a high thrust prop.
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version
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Akenumber
Navigator

Members Avatar

USA
247 Posts
Response Posted - 11/22/2015 :  18:18:21  Show Profile
I done know about top end, but I am a huge fan of the high thrust prop. So much more control when docking and stopping the boat. I notice it pushes better in rough water too. I would say it's worth the try. I think mine is a solas
Ken
San Diego
84 C25 SR/FK 4116
The KRAKEN
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sailboat
Navigator

Members Avatar

USA
149 Posts
Response Posted - 11/22/2015 :  21:03:30  Show Profile
Thanks. Do you have any specs and or price on the Solas?
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version
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pastmember
Master Marine Consultant

Members Avatar

2402 Posts
Response Posted - 11/23/2015 :  12:54:54  Show Profile
I tried one and it was worse around the dock where it was supposed to be better and I lost top speed. Took it off.
Frank Hopper
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sailboat
Navigator

Members Avatar

USA
149 Posts
Response Posted - 11/23/2015 :  16:48:16  Show Profile
That is what I like...empirical evidence. This forum and the sailboat owners forum gave mixed results and much speculation. I'll adjust the tow length and keep the C-25 hull clean. Cheers, Mike
Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version
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Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9013 Posts
Response Posted - 11/23/2015 :  20:54:06  Show Profile
quote:
Originally posted by pastmember

I tried one and it was worse around the dock where it was supposed to be better and I lost top speed. Took it off.
That doesn't come close to my experience, but I was comparing a 199X Honda 8 with a "standard" prop, with a 2002 "Power Thrust" Honda 8 (prop, gearing, and other mods by Honda). Big improvement.
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
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Akenumber
Navigator

Members Avatar

USA
247 Posts
Response Posted - 11/24/2015 :  21:59:16  Show Profile
Whoh, whoh, my experience was an 8hp yamaha 4 stroke oe prop. Hated it. Then merc 2 stroke with oe prop and it at least idled. Merc with Solas, very happy. Mostly when I put it in reverse it actually stops or reverses. It's physics. Unless someone acquired one that was used and damaged I don't understand how you could not have bottom end gain.
Ken
San Diego
84 C25 SR/FK 4116
The KRAKEN
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.