Association Forum - 15hp vs 9.8 hp outboards

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

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.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

15hp vs 9.8 hp outboards

New Topic

Topic Locked

Printer Friendly

Author

Topic

cat78
1st Mate

Member Avatar

34 Posts

Initially Posted - 01/29/2004 : 16:03:55

I am presently using a mercury 9.8 ob with an sail prop on my c25. I am getting about 5-6 knots out of it. I was wondering if any one was using a 15hp and what type of speed they were getting out of it.

dave
passing wind

Edited by - on

Leon Sisson
Master Marine Consultant

Members Avatar

USA
1893 Posts

Response Posted - 01/29/2004 : 16:25:46

dave,

Five or six knots is about all you're gonna get out of a Catalina 25 hull, no matter how much horsepower you apply. These are displacement hulls with a hull speed around 6.5 knots. They don't slice or plane through the water like a Hobie cat, Sunfish, or ski boat.

I have a 10HP high trust outboard, and I cruise under motor around 4 to 5 knots at maybe half throttle or less. Turning up the power just makes more wake and sucks more fuel.

If you'll look around just a bit on these Catalina 25/250 forums, you'll find a very recent discussion about whether 10HP is even needed, or if 8HP would be plenty with the right prop.

-- Leon Sisson

Edited by - on

matsche
Captain

Members Avatar

USA
280 Posts

Response Posted - 01/29/2004 : 20:05:47

I had a 15hp Mariner that I traded in for a 6hp Tohatsu. I much prefer the Tohatsu. I couldn't get more than about 6-6.5 knots out of the 15hp with the rear end dragging and putting out a lot of wake. I would typically cruise nicely at 4-5 knots. The 6hp will do that at 1/2-3/4 throttle. Our C25s just don't make good ski boats!

Edited by - on

dlucier
Master Marine Consultant

Members Avatar

Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 01/29/2004 : 20:43:25

I agree with what Leon and John have said, a 15hp would just me a waste of horsepower, weight, and $$$$. My 8hp Mercury is plenty for me on Lake Erie and I reach hull speed a little over half throttle.

Keep your 9.8 Mercury and spend the money on other toys!

Edited by - on

Bill Holcomb
Admiral

Members Avatar

USA
769 Posts

Response Posted - 01/30/2004 : 09:17:39

Hi Dave,
Snickerdoodle has a 15 hp Mariner on her. The reason that I bought the Mariner was that the 7.5 hp Honda that I purchased new when I bought the boat new was destroyed in it's last tune-up. Long story here.....

Anyway, the reason that I bought the 15 hp Mariner was that it has an electric start and weighed in around 20 lbs less than the 7.5 Honda. And, was immediately available. I needed an engine on the boat for the next day.

At full throttle, the boat will plow through the water at hull speed, ~6.3 knots, and sucks fuel like crazy. At 5 knots though, the engine is running quietly and uses a little less than 3/4 gallon per hour.

BTW: When I bought Snickerdoodle in 1985, Catalina suggested that the appropriate engine size was between 7.5 and 10 hp. I believe that is a good recommendation.

Bill Holcomb - C25 Snickerdoodle #4839

Edited by - on

Dave Bristle
Master Marine Consultant

Members Avatar

Djibouti
10005 Posts

Response Posted - 01/30/2004 : 21:40:45

Dave: By the time you get to hull speed (about 6.3 kts), an outboard is pushing the the stern down (creating drag) due to simple leverage, and the bow wave is pushing back as hard as the engine can push against it. You'll need something like 50 hp to get you beyond that speed, at which point your bow will be pointed at the sun. Just getting to hull speed, even with 8 hp, is highly wasteful compared to running at about 5 kts, where the boat isn't challenging its bow wave and the motor isn't making the transom drag.

5-6 is how fast a 25-footer goes. Enjoy it.

Edited by - on

lcharlot
Master Marine Consultant

Members Avatar

Antigua and Barbuda
1301 Posts

Response Posted - 01/30/2004 : 22:13:41

8 hp is generally enough power for a C-25 in calm conditions, 10 hp with a high thrust prop is nice when you have to beat home against a headwind or in choppy conditions. I have noticed that my new boat, #5857, which has an older Honda 7.5, hits a powerboat wake, it pretty much stops dead in the water and has to accelerate again from scratch after the wake passes, whereas my old boat, #1205, that has a Honda 10, seems to power through wakes without losing so much speed.

Edited by - on

DocNeon
Deckhand

Members Avatar

USA
23 Posts

Response Posted - 02/04/2004 : 14:29:03

Dave
The replies pretty much cover what I was going to say - displacement hull - max speed, etc. When it came time to replace my 9.9 Johnson Sail Master on my ex C25 some time ago, I ended up with a 15 Johnson long shaft - year previous model - as that was all my supplier had in stock. He sold it to me for the same $$ as the 9.9 to clear his inventory. I went ahead and took the deal...but ONLY because he offered such a great price.. Speed? Gas Consumption? All about the same as the 9.9. Additional weight I guess, but that never seemed to be a factor. All said and done - I'd go with the least horsepower needed to reach max hull speed..I still think an 8 hp <+ or -> would accomplish the same goal.

Regards

Edited by - on

DocNeon
Deckhand

Members Avatar

USA
23 Posts

Response Posted - 02/04/2004 : 14:33:07

Oh.. also.. forgot to mention.. I was told of a fairly new product called a "prop thruster" <dont hold me to the name> . I believe its available thru sailboatowners.com.. No experience with the thing, but I'm told it is a great device to increase thrust.

Edited by - on

tmhansen
Captain

Members Avatar

USA
397 Posts

Response Posted - 02/05/2004 : 02:05:44

My boat came with a 15 hp motor. I can't offer a comparision with a lesser motor other than what the manual for my Evenrude says. The 9 and 15 are the same weight, same block. The 9 has a higher output on the alternator than my 15. I would think that hull speed is hull speed but the extra umphf will help in head winds and chop. Note a bigger motor will not help in currents as the hull speed through the water is the limiting factor.

Edited by - on

Dave Bristle
Master Marine Consultant

Members Avatar

Djibouti
10005 Posts

Response Posted - 02/05/2004 : 20:05:13

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by DocNeon
 ...I was told of a fairly new product called a "prop thruster" ...
<hr height="1" noshade id="quote"></blockquote id="quote">
I think that's Garhaur's product. It's purpose is to compsensate for the prop pitch being too high for the boat speed, which is a temporary condition with a planing hull as it gets started, and a permanent condition with our heavy displacement hulls if we have the wrong (standard) prop. The most important upgrade you can make to your C-25 outboard is a low-pitch prop--ideally as large in diameter as you can fit below the anti-cavitation plate. The ideal pitch is based on the speed the boat will be moving through the water, and ours never gain much more than 5 knots--a small fraction of the speed of the small, planing boat the standard prop was designed for.

Edited by - on

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

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.