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Catalina/Capri 25/250 Sailor's Forums

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How much horsepower for a dinghy?

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OJ
Master Marine Consultant

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USA
4382 Posts

Initially Posted - 12/06/2009 : 01:30:37

Have an 8' Walker Bay dinghy and recently made an offer on a 2 HP 2 stroke motor. When I explained what I was going to use it for - the seller kindly explained that he felt 2 HP was too small, even for an 8' hull.
Before I consult the manufacturer, anyone have experience sizing a motor for a dinghy?

Edited by - OJ on 12/06/2009 01:31:34

delliottg
Former Mainsheet C250 Tech Editor

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Response Posted - 12/06/2009 : 02:03:54

Unless you're a small guy, a 2hp is unlikely to push your WB up onto plane, but it'll certainly get you where you want to go in a small economical package. We have a 5hp for our Avon 3.15 (10'-3"). It can't push me up onto plane in the Avon, but it probably could for Rita (she's much smaller than I am). It's light enough to carry around, but for as little as I use it, I'd be pretty happy with a 2hp simply because of the lower weight to pack around. A 5hp might be able to push your WB up onto plane, maybe, depending on the load.

I kinda like rowing our dinghy around, so our outboard's not so important to me.

Edited by - on

islander
Master Marine Consultant

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Response Posted - 12/06/2009 : 07:17:48

A 2HP will move the boat along. Fine for say ship to shore or just exploring but definitely no planing. I have an 8ft inflatable that I originally had a 5HP Yamaha on it. It would plane with me alone (185lbs) but not with two people. Then I put an 8HP Yamaha on it and it would plane with me and my wife, but not two men. It all depends on how you intend to use the boat. A 2HP will be much lighter if you intend to break the tender down and hang on a rail and probably has an internal gas tank so there isn't the need to carry an extra tank and fuel hose with you. I also don't know just how big of a motor you could hang on a rail but a 2HP should be fine.

Edited by - islander on 12/06/2009 10:34:03

britinusa
Web Editor

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Response Posted - 12/06/2009 : 08:15:01

We've been looking at 2.5hp for our 8'6" inflatable, I think the max is 4.5hp according to the manufacturers (ZRay Inflatable) No plans on planning! It's primarily for ship to shore and ship to ship. Right now the only power is an inboard 1mp.

Paul

Edited by - on

OJ
Master Marine Consultant

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Response Posted - 12/06/2009 : 08:43:51

Very good points - thank you Paul, Scott and Dave. This will be a ship-to-shore and exploring vehicle. Two adults will be the norm - I'm more concerned about currents than anything. Yes, rail mount is the plan. While internal tanks are convenient they tend to be a wee-bit small so I'm probably stuck carrying a spare can. Maybe a 3 1/2 horse in a better choice? Does anyone know if the smaller 4-stroke motors have high thrust blades like the 9.9 models . . . and if so does that offset the additional weight?

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OJ
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Response Posted - 12/06/2009 : 08:46:03

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by britinusa
 . . . right now the only power is an inboard 1mp.

<hr height="1" noshade id="quote"></blockquote id="quote">

It's an Armstrong?

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 12/06/2009 : 09:01:48

I run a Honda 2 on my 8'6" inflatable, and it would seem to easily push the boat to hull-speed... By that I mean there's a throttle point past which the boat doesn't go any faster--it just torques down the transom. That tells me that except for going on plane (which obviously it won't), more power would do nothing for me, even against a current. (Hull-speed is what it is, relative to the water, so I need to avoid 4+ knot currents.)

A friend bought the new Suzuki 2.5, which is virtually the same weight as the Honda: 28-29 lbs. (Nothing else on the market comes close at this point.) The Suzuki is water-cooled, which makes it a little quieter, and has a F-N shift compared to the Honda's centrifugal clutch. I'd prefer the shifter. The Honda's air-cooling makes it simpler, but noisier. Both have internal tanks, which I like. Another friend has a Honda 5 on a similar inflatable--it doesn't plane and goes no faster than my 2, unless maybe both boats had four people in them. (I haven't had four in mine.) The 5 uses an external tank, a pain on a tender IMHO.

Edited by - Dave Bristle on 12/06/2009 09:44:33

Dave Bristle
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Djibouti
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Response Posted - 12/06/2009 : 09:29:59

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by OJ
 ...Does anyone know if the smaller 4-stroke motors have high thrust blades like the 9.9 models . . . and if so does that offset the additional weight?<hr height="1" noshade id="quote"></blockquote id="quote">The Honda 2 has a prop that is apparently designed for what I do--push a small boat to hull speed well within its RPM limit. The 8 and 9.9 have high-thrust props for pushing large displacement hulls to hull-speed, and "standard" props for pushing smaller boats onto plane. So I'd say the little 2-3 hp engines effectively have high-thrust props designed for what they normally do.

Edited by - Dave Bristle on 12/06/2009 09:30:38

Renzo
Admiral

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Response Posted - 12/06/2009 : 09:34:04

OJ, I, also have a Walker bay 8 and I think if you check the plate on the inside of the transom you will find that the max size OB recommended by the mfg is 2HP. If your WB-8 doesn't have the optional floatation collar I would stick with the 2HP limitation for safety sake. The WB-8 is a great dingy for rowing and sailing but it is tender and has weight restrictions. The 2hp will do just fine for general duty unless you want to use it like a PWC.

Edited by - on

OJ
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4382 Posts

Response Posted - 12/06/2009 : 09:45:52

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Renzo
 . . . the 2hp will do just fine for general duty unless you want to use it like a PWC.

<hr height="1" noshade id="quote"></blockquote id="quote">

PWC, hmmm, never thought of that option. Then I could generate wakes around motor boats anchored in quiet coves!

Payback has its rewards!

Edited by - OJ on 12/06/2009 09:47:33

islander
Master Marine Consultant

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Response Posted - 12/06/2009 : 10:23:42

The 2HP will go a long way on the internal tank. You can always carry a spare gal. container as a back up if needed. I would be more concerned about the weight of the engine. You are going to have to put it on and off the dink. For that reason alone I would go with the 2hp. With mine I used one of these http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?resultCt=1& jspStoreDir=wm51& catalogId=10001& productId=17867& keyword=214876& y=8& x=42& storeId=10001& ddkey=SiteSearch It has a handle on top so you can pick the motor up like a suitcase with one hand.and keep the other hand on the boat. It really helps in making an awkward maneuver easer.

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 12/06/2009 : 10:49:35

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by islander
 ...With mine I used one of these... It has a handle on top so you can pick the motor up like a suitcase with one hand...<hr height="1" noshade id="quote"></blockquote id="quote">Looked like a great idea until I saw "Not for air-cooled engines."

Edited by - on

islander
Master Marine Consultant

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4018 Posts

Response Posted - 12/06/2009 : 11:12:06

Dave, I saw that too. I haven't looked at a Honda air cooled motor so I don't know why its not recommended.

Edited by - on

mlg3733
Navigator

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118 Posts

Response Posted - 12/06/2009 : 11:18:09

The Walker Bay is rated for 3 hp and 260 lbs, I have a Colt (1.2 HP) on mine and it moves two people easily enough, but I feel that a 2 HP would be better, particularly on choppy days.

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Rich P
1st Mate

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USA
77 Posts

Response Posted - 12/06/2009 : 11:24:58

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by OJ
PWC, hmmm, never thought of that option. Then I could generate wakes around motor boats anchored in quiet coves!

Payback has its rewards!

<hr height="1" noshade id="quote"></blockquote id="quote">

Gotta be prepared:
http://www.amazon.com/Northern-Tool-Equipment-ask-100-Slingshot/dp/B000QFDKYM

Edited by - on

OJ
Master Marine Consultant

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4382 Posts

Response Posted - 12/06/2009 : 12:08:04

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Rich P
 [quote]Gotta be prepared:
http://www.amazon.com/Northern-Tool-Equipment-ask-100-Slingshot/dp/B000QFDKYM
<hr height="1" noshade id="quote"></blockquote id="quote">

Yep, already got one of those for my split backstay . . . and I use the windlass to draw the payload all the way back to the v-berth bulkhead!

Edited by - on

Nautiduck
Master Marine Consultant

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3704 Posts

Response Posted - 12/06/2009 : 12:29:20

We have an Evinrude 2hp on our WB 10. It is plenty of power. Key is light weight for putting the outboard on and off. We have the RIB kit (flotation tubes) and I highly recommend it. With the tube kit the WB is still easy to row but also becomes very stable. The perfect dink for us.

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crcalhoon
Captain

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USA
303 Posts

Response Posted - 12/06/2009 : 15:39:58

I used to have an 8'6" inflatable. First I had a 3 HP British Seagull which was noisy and messy, but plenty powerful. I "upgraded" to a Yamaha 4 HP and although I never really regretted it, I thought of the Seagull every time I hoisted that 4 HP up to the rail. I think 2 or 3 HP is plenty for a small dinghy. It is kind of debatable (don't want to start something here) as to whether any small dinghy/motor combo will do you much good in adverse conditions, i.e. wind, tide, current.

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DaveR
Master Marine Consultant

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USA
2015 Posts

Response Posted - 12/07/2009 : 09:35:07

I've got an 8ft Quicksilver with a 06 Suzuki 2.5 4 stroke (water cooled). Get's me on plane by myself, is light, get's great mileage so the onboard gas tank is fine. Very happy with it.

Edited by - DaveR on 12/07/2009 09:35:34

OJ
Master Marine Consultant

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4382 Posts

Response Posted - 12/07/2009 : 17:39:34

A moderate to strong current is my biggest concern here. I know the powerhead for a 9.9 and 15 are the same - just different carburation for the most part. I wonder if the same is true for the Johnson 2 and 3.5 horsepower models. Same weight with extra oomfh.

You guys are great - sharing your experiences, thoughts - even pix! Thanks

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