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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

8 HP outboard or upgrade to a 15HP

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Stingray Meg
Deckhand

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USA
19 Posts

Initially Posted - 11/18/2008 : 15:13:30

Hey folks. I currently have a Johnson 8 HP on Meg C25 fixed keel.

We generally just cruise no racing for Meg. When I have to motor I usually move along at 4.5 to 5 knots, this is with the 8 HP at 3/4 to full throttle. Motor is a long shaft.

I have an chance to buy a Mercury 15 HP long shaft approx. same weight as a 9.9 HP for a decent price and I was wondering if you folks thought it would be a good idea? My goal is to get maybe 5.5 to 6 knots crusing speed when I have to motor. Plus we generally carry a fair amount of weight onboard with My wife, two boys, toys, water, food, and beer for our trips.

Any thoughts? concerns?

Thanks.

'79 Catalina 25 FK/SR # 1203

Edited by - on

kaferhaus
1st Mate

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40 Posts

Response Posted - 11/18/2008 : 15:53:09

unfortunately, all you're going to do is burn more gas...

I tried a 15 on my 25 (a friends) and got nothing...

Put the 9.9 Honda back on it.

Edited by - on

Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 11/18/2008 : 16:10:41

My C25 had a Merc 7.5, and it pushed the boat as fast as any of my friends' boats. The weight of provisions and crew don't have much effect on a displacement boat. I agree that the main difference is that the 15 will use more fuel.

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 11/18/2008 : 18:44:02

As the others have stated, on our boats, more horsepower doesn't really equate to more boat speed.

Edited by - on

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 11/18/2008 : 18:55:29

Everything I've read indicates that 15 is wasted horsepower. My 9.8 Nissan will push it to hull speed quite easily and nowhere near full throttle.

Edited by - dmpilc on 11/18/2008 18:56:01

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 11/18/2008 : 19:28:09

The sweet-spot for the iron genny on a C-25 is around 5-5.5 knots. Above that, the boat begins to squat astern, drawing a bigger wake that creates drag. Our Honda 8 pushed Passage to above 5 knots at maybe a little over half throttle--to get to six would've taken the other half--burning more fuel and making more noise for maybe 3/4 of a knot.

I don't know how the chop and wakes are on your lake, but in general I'd recommend an extra-long (usually spec'd as 25") shaft over an increase in HP, and a four-stroke for quieter cruising with no fumes. If the Merc 15 is a 20" 2-stroke, I think it's a poor investment.

Edited by - on

bigelowp
Master Marine Consultant

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USA
1776 Posts

Response Posted - 11/18/2008 : 22:48:30

I concur with the above posts -- 15 hp is more than is needed or ideal. I have a 9.8 Tohatsu and have never needed more than half throttle . . . and consumed 1/2 of my 3 gal tank during the entire (five month) 08 season! Stick to an 8-10 hp and I also agree that a 25 inch is the way to go on our boats.

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 11/19/2008 : 06:49:08

15 is just going to make more noise and burn more fuel. Have you considered switching the prop?

Edited by - on

Stingray Meg
Deckhand

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USA
19 Posts

Response Posted - 11/19/2008 : 07:24:18

Thanks folks! I will look into the prop situation as I really don't know what my prop situation is. Meg's due for a bottom painting this winter/spring as well, that will certainly help.

It is a unanimous opinion that the 15 will not give me better speed on the days when the wind won't blow... so I'll keep the 8 HP and concentrate on the other needs of Meg.

Thanks again everyone!

Edited by - on

Sloop Smitten
Master Marine Consultant

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USA
1181 Posts

Response Posted - 11/19/2008 : 08:32:44

If your running at 3/4 throttle with an 8HP outboard and only getting 4.5 to 5 knots I would move up the date of my paint job. It sounds like you might have an excessive amount of growth on the keel. Been there. I would expect you to be at hull speed (6+ Knots) at 3/4 throttle.

Edited by - on

millermg
Navigator

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159 Posts

Response Posted - 11/19/2008 : 23:37:52

If anyone is curious, heres' a scientific explanation of why 15 hp is no better than 8 hp on a 25' sailboat: http://www.solarnavigator.net/hull_speed.htm
I get hull speed at about 1/3 throttle w/ my honda 8. 3/4 throttle would get me maybe another 1/2 knot.

Edited by - on

Ed Cassidy
Captain

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USA
365 Posts

Response Posted - 11/20/2008 : 08:43:52

Would it be safe to say that the advantage of a 15HP outboard would be that it would get you to hull speed quicker and that in reverse, it would stop you quicker? With the correct prop of course.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 11/20/2008 : 08:47:04

Hate to say it, but that treatise on the physics of hull-speed is a strange interpretation of whatever he's been reading, and his "calculator" doesn't gibe with the widely accepted formula of 1.34*sqrt(LWL). Theoretical hull speed is reached when the bow wave is swept back to an angle where its wavelength, measured in the direction of the boat, puts the boat dead-center between two crests, such that it must "climb out" in order to go any faster. The power to make it climb is also enough to create pressure on the bow sufficient to push it up out of the water, into "semi-displacement" mode. That takes some multiple (which depends on the hull form) of the power needed to reach hull-speed. There are special exceptions--for example, the very slender, knife-shaped hulls on Frank's Hobie.

Here's a [url="http://boatsafe.com/nauticalknowhow/waves.htm"]better explanation[/url].

Edited by - Dave Bristle on 11/20/2008 09:10:15

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 11/20/2008 : 08:51:49

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Ed Cassidy
 Would it be safe to say that the advantage of a 15HP outboard would be that it would get you to hull speed quicker and that in reverse, it would stop you quicker? With the correct prop of course.
<hr height="1" noshade id="quote"></blockquote id="quote">To some extent. But my high-thrust Honda 8 accelerated my C-25 very adequately, and stopped her like she'd run into a pillow. If I went to full-throttle to do either, it would cavitate.

It can be said that higher hp will be able to overcome heavier head-winds and bigger waves on the nose, since those work against you independently of the hull-speed affect. It doesn't have any advantage against a current--your hull speed is "through the water" whatever speed it's going--not "over the bottom".

Edited by - Dave Bristle on 11/20/2008 08:55:30

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 11/20/2008 : 09:53:23

I just found this site with some really good Johnson 9.9 info.

http://www.sschapterpsa.com/ramblings/OMC/OMC%20info.htm

I've added it to my bookmarks asa I try to figure out the lower unit oil leak I'm now very obviously suffering - evidenced by the gear oil I just put in th eengine being in a puddle on th ebasement floor...

One of the tidbits on it is:

Difference between the 9.9 & 15hp : When they designed this series of motors, they designed it as a 15 hp & then detuned it with a different carburetor for the 9.9. When the 9.9hp and 15hp came into being in 1974 and up thru 1978, the only real difference between the two motors was the carburetor. In 1979 they added a shim, part #325038, (one for each cylinder), behind the leaf valves & under the stop plate for the 15 hp, apparently to allow the motor to suck more fuel & air mixture in.

The outside visual dimensions of both carburetors appear the same, unless you look inside the throat. If you look in from the rear, you will have to position the throttle plate to a horizontal position to be able to see the throat very well. The 9.9 hp carburetor’s internal throat is .625 dia., 15 hp internal throat is .875 dia. up until late 1987 when they went to a plastic topped carburetor. The outlet or rear throat dia. is the same on both to match the manifold port dia. The idle jet venturi system is also slightly different between the two. The part number for the the pre 1987 9.9 hp Carburetor Assembly is #388936, while the 15 hp Carburetor Assembly is #338273. This increased throat dia. & larger main jet allowed it to breather better & pull more fuel in, increasing the RPM about 1000 RPM."

So if you find a great deal on a Johnson/Evinrude 15HP, it can be relatively easily converted to a 9.9 saving your fuel costs. Just a tidbit worth knowing.

Edited by - on

Stingray Meg
Deckhand

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USA
19 Posts

Response Posted - 11/20/2008 : 10:14:40

Dave, I think you hit the crux of my most recent problems with speed. Going upriver, head wind, and tidal flow..

very interesting information from everyone..

Edited by - on

Stingray Meg
Deckhand

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USA
19 Posts

Response Posted - 11/20/2008 : 10:19:32

wow a 9.9 and 15 basically same engine, with a diferent carb.. kind of like restrictor plate racing in nascar, wonder if the reverse would also be true, putting the 15 carb on the 9.9 motor to in effect make it a 15 HP motor?

Edited by - on

pastmember
Master Marine Consultant

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2402 Posts

Response Posted - 11/20/2008 : 10:28:32

I understand the Nissan 8 and 9.8 are the same engine in the modern 4 stroke world. Which explains it's lightness.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 11/20/2008 : 11:44:21

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Stingray Meg
 ...wonder if the reverse would also be true, putting the 15 carb on the 9.9 motor to in effect make it a 15 HP motor?<hr height="1" noshade id="quote"></blockquote id="quote">I don't know about the Johnson, but a Honda rep told me that the primary difference between the Honda 8 and 9.9 (same block, drive-line, prop, and casing) is that the 9.9 is cammed for higher RPMs and hp, while the 8 is cammed for more low-end torque, and doesn't rev as high. (He was suggesting the 8 was a better choice for a heavy sailboat.) So there might be more differences on the Johnson than just the carb--or not.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 11/20/2008 : 12:08:06

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Stingray Meg
 wow a 9.9 and 15 basically same engine, with a diferent carb.. kind of like restrictor plate racing in nascar, wonder if the reverse would also be true, putting the 15 carb on the 9.9 motor to in effect make it a 15 HP motor?
<hr height="1" noshade id="quote"></blockquote id="quote">

May be true - but as Dave pointed out - there may be other differences, perhaps prop size, maybe bottom end stuff?? Who knows, this is someone's personal web page we are referencing, not information from OMC/Bombardier.

I suspect that your statement is right though. But it is kind of a moot point since you said above that your engine is a 8HP. If on the other hand you find a deal on a Johnson, you may be able to try it as both 15HP and 9.9HP - just verify with a trusted mechanic that the statement I posted is true, and check on the year of manufacture to be sure it falls in "the zone".

Edited by - Prospector on 11/20/2008 12:09:48

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 11/20/2008 : 12:37:35

Frank, you are correct. The Nissan 8 and 9.8 are the same engine, with just slight modifications to create the difference in hp. Also, the 8 is a little bit less expensive. Unfortunately, the 8 is not available in both 25" shaft and electric start (at least from OnlineOutboards), which is why I bought the 9.

Edited by - on

Deltarat
1st Mate

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USA
69 Posts

Response Posted - 11/21/2008 : 00:49:42

I'm looking at getting a 93' honda 9.9 4 stroke for my c25. I'm told it is a long shaft motor off of a 26' sailboat, but I was wondering does honda sell a retro kit to make it a 25" longshaft? Does anyone have any experience with this kind of upgrade?

Edited by - on

kaferhaus
1st Mate

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40 Posts

Response Posted - 11/21/2008 : 18:01:09

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Deltarat
 I'm looking at getting a 93' honda 9.9 4 stroke for my c25. I'm told it is a long shaft motor off of a 26' sailboat, but I was wondering does honda sell a retro kit to make it a 25" longshaft? Does anyone have any experience with this kind of upgrade?
<hr height="1" noshade id="quote"></blockquote id="quote">

No kit. You have to change the shift shaft, waterpump driveshaft and there's a spacer that gets you the 5"

If I remember correctly when I looked into it the parts were well over $300.00

Honda's are great motors but the parts prices are rediculous. And unfortunately it's near impossible to find any aftermarket parts for them either.

I have a terrible time just finding spark plugs for my 2005 9.9...

But I love the engine... it can sit for months and start on the first pull.

Edited by - on

Chris Z
Captain

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452 Posts

Response Posted - 11/21/2008 : 20:08:26

I bought a 15 carb. Removed two bolt and linkage and then bolted the new one in place and hooked up the linkage.

The image shows the extra bowl that kicks in once the linkage goes so far.

The boat has much more power. Also, I was surprised that I didn't have to change anything else or fine tune it. I have been running for about 5 years and love it.

On another note, I found this picture also while looking for the other ones. This makes filling the lower unit a breeze.

Edited by - on

Deltarat
1st Mate

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USA
69 Posts

Response Posted - 11/21/2008 : 20:43:21

Well since I'm only paying $600 for the engine an extra $300.00 may be worth it to have the motor in the water all of the time.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by kaferhaus
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Deltarat
 I'm looking at getting a 93' honda 9.9 4 stroke for my c25. I'm told it is a long shaft motor off of a 26' sailboat, but I was wondering does honda sell a retro kit to make it a 25" longshaft? Does anyone have any experience with this kind of upgrade?
<hr height="1" noshade id="quote"></blockquote id="quote">

No kit. You have to change the shift shaft, waterpump driveshaft and there's a spacer that gets you the 5"

If I remember correctly when I looked into it the parts were well over $300.00

Honda's are great motors but the parts prices are rediculous. And unfortunately it's near impossible to find any aftermarket parts for them either.

I have a terrible time just finding spark plugs for my 2005 9.9...

But I love the engine... it can sit for months and start on the first pull.
<hr height="1" noshade id="quote"></blockquote id="quote">

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 11/21/2008 : 21:02:03

A common upgrade in the early Honda 4 stroke days was converting a 10Hp engine to 15hp... all it took was a carb jet and camshaft. Cost of the upgrade was about 1/2 the difference in price between the two models.

Edited by - on

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