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Old 05-12-2016, 10:11   #91
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Re: inboard vs. outboard for cruising

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Originally Posted by donradcliffe View Post
The best engine is a diesel inboard. Better fuel mileage, no gasoline fume hazards, better alternator, more reliable, and you can work on it inside the boat.
Totally agree with the above. But, if starting without a working engine and the initial cost is critical, outboards are a lot cheaper to buy, install, and repair. Also if you need to allow for covering a lot of miles before refueling storing sufficient gas might be even more important than the greater cost per mile.
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Old 05-12-2016, 11:00   #92
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Re: Inboard vs. Outboard for Cruising

Are those quoting diesel fuel efficiency numbers taking into account that if you're looking at an outboard vs inboard, you're most likely looking at a very old inboard, and that there will be major real life inefficiencies to an inboard? Off the top of my head: inboard no longer running at peak fuel efficiency due to age, a vertical decline in the prop shaft to get the prop in the water, a lateral offset to the prop in order to be able to drag the prop shaft out past the rudder and/or work on the prop. With these three characteristics on my boat, my 11 HP diesel moved the boat about a half knot faster than my current 6 HP outboard. Never tested the fuel efficiency.

But you'd have to motor a hell of a lot to make that fuel efficiency number matter, and you would have to own your boat for a lifetime to reap the benefits of a more durable diesel.

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Old 05-12-2016, 11:05   #93
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Re: Inboard vs. Outboard for Cruising

Connemara (27 foot Mirage) has the old OMC Johnson saildrive and I've seen it replaced by an OB. I was told it needed a really long leg and a very robust mount with extra bracing.

But even then I think in heavy water the prop would be out of the water half the time.

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Old 05-12-2016, 11:08   #94
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Re: Inboard vs. Outboard for Cruising

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Connemara (27 foot Mirage) has the old OMC Johnson saildrive and I've seen it replaced by an OB. I was told it needed a really long leg and a very robust mount with extra bracing.

But even then I think in heavy water the prop would be out of the water half the time.

Connemara
If the prop is coming out of the water, there is usually wind.

If there is wind, raise the sails then turn the outboard off and raise it out of the water

So far this approach has worked for me. Once in a narrow channel it was a bitch but I was able to sail out tacking multiple times then crossing a bar ....... barely (got tired of tacking and figured I could make it)
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Old 05-12-2016, 11:17   #95
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Re: Inboard vs. Outboard for Cruising

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If the prop is coming out of the water, there is usually wind.
You'd think so. But it's not always the case, especially after thunderstorms on Lake Ontario. And you might have to motor into the wind for any one of a number of reasons. Or you might have damaged your sails in the enormous wind that is blowing and be unable to sail.

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Old 05-12-2016, 12:06   #96
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Re: Inboard vs. Outboard for Cruising

i wonder how much of this topic has to do with

1. full keel vs fin
obviously, if you have full keel the boat won't handle the same way as fin in tight quarters.

2. sailing background
For instance, I learned to sail as a kid on a sunfish and sailed in and out. If I started as an adult, I would no doubt be on a bigger boat and had an engine. The way I look at it is that I'm on a sailing vessel first. My eye is even when the engine is running always thinking "where is my out" about what to do if the engine dies. Kind of like chess, X moves ahead.
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Old 05-12-2016, 12:09   #97
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by brownoarsman View Post
Are those quoting diesel fuel efficiency numbers taking into account that if you're looking at an outboard vs inboard, you're most likely looking at a very old inboard, and that there will be major real life inefficiencies to an inboard? Off the top of my head: inboard no longer running at peak fuel efficiency due to age, a vertical decline in the prop shaft to get the prop in the water, a lateral offset to the prop in order to be able to drag the prop shaft out past the rudder and/or work on the prop. With these three characteristics on my boat, my 11 HP diesel moved the boat about a half knot faster than my current 6 HP outboard. Never tested the fuel efficiency.

But you'd have to motor a hell of a lot to make that fuel efficiency number matter, and you would have to own your boat for a lifetime to reap the benefits of a more durable diesel.

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Near hull speed resistance goes up sharply.

Assuming 9200lb, 24' lwl then the 6hp should get you right to hull speed in flat water.

Per the Skene's speed to thrust graph 11hp should get you an extra 0.4kt or so. If you had a 9.9hp outboard it would probable perform a bit worse than the inboard but measurably better than the 6hp. This small speed difference has little to nothing to do with outboard vs inboard, its about being past hullspeed and getting very little to show for any extra power you expend.

The 11hp inboard should maintain a significantly better speed going into wind and/or waves.

The real difference will be in fuel economy. You really want to check it at 4kt & 5kt.
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Old 05-12-2016, 12:16   #98
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by boatsail View Post
i wonder how much of this topic has to do with

1. full keel vs fin
obviously, if you have full keel the boat won't handle the same way as fin in tight quarters.

2. sailing background
For instance, I learned to sail as a kid on a sunfish and sailed in and out. If I started as an adult, I would no doubt be on a bigger boat and had an engine. The way I look at it is that I'm on a sailing vessel first. My eye is even when the engine is running always thinking "where is my out" about what to do if the engine dies. Kind of like chess, X moves ahead.
Valid points....

1. The outboard definitely helps with maneuvering in tight quarters on a full keel boat.

2. My first 4 sailboats didn't have engines and I mostly raced them. (Beachcats. Hobie 2X, Nacra 2X)

I must say though the engine certainly comes in handy when the wind drops or if you need to use it to help you point to get back. I got my fill of drifting around waiting on the wind
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Old 05-12-2016, 12:43   #99
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Inboard vs. Outboard for Cruising

Quote:
Originally Posted by boatsail View Post
i wonder how much of this topic has to do with

1. full keel vs fin
obviously, if you have full keel the boat won't handle the same way as fin in tight quarters.

2. sailing background
For instance, I learned to sail as a kid on a sunfish and sailed in and out. If I started as an adult, I would no doubt be on a bigger boat and had an engine. The way I look at it is that I'm on a sailing vessel first. My eye is even when the engine is running always thinking "where is my out" about what to do if the engine dies. Kind of like chess, X moves ahead.

This is an internet forum, the thread is about whatever the current consensus/posts/whatever make it. You just brought up fin vs full so it is now at least a little bit about that.

I learned to sail on dinghies too then graduated to small keelboats with unreliable motors so I too acquired that habit. Now when I take my best friend off sailing in stupid places off season his wife says she never worries about him, she says I have backup plans for my backup plans and sometimes backup plans for those too.

The plan for the current boat is a 4hp in a motorwell with 12gal or 18gal fuel which at 4kt should push the boat 216 or 324nm, 400-500nm at 3kt. Backup is going to be a 30lb thrust trolling motor with 3 or 4 extra solar panels which should push the boat at almost 4kt.
Backup to that will be a 10' or so oar. If I can figure out storage I may try to build a yuloh.

Assuming 12h days trolling at 3kt and motoring at night at 4kt that's 84nm/d. I'd make it 9d and about 750nm before running out of fuel.
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Old 06-12-2016, 23:13   #100
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Re: Inboard vs. Outboard for Cruising

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That's the kind of info that is needed.
Bet you don't have to run the 4 HP at as high of rpm as you did with the 3.5 and that means better fuel economy. Also you are right the high thrust prop makes a heck of a difference to.
It's not a monohull but our gemini at 6.5kt cruise:
- Original 40hp 2 stroke: 3MPG
- New 25hp 4 stroke: 6-7MPG (if we dropped back to 4-5kts we could bump that up to well over 10MPG but other than a bit of testing it's not worth the trouble).
- Reports from others with 27hp diesel: 8-9MPG

Yes, diesel does do better on fuel consumption but when you factor in the up front cost and ongoing maintenance, (and yes the diesel is much higher) you have to do a LOT of mile for the fuel savings to pay off.

With 2 built in tanks and an outboard tank on a 3 way valve (this is how it came), we had over a 300mile range under power with has always been plenty.

Also being a catamaran, the tanks are bottom vented to the airspace between the hulls so no issues with gas fumes getting down into the bilge.
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Old 07-12-2016, 14:38   #101
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Re: Inboard vs. Outboard for Cruising

Not deliberately setting out to take this tread in any different direction..BUT...I read this thread because the boat I am refitting came into my possession with all previous engines removed.( & the rig taken down for that matter) However also in stock we have a 9.9 Honda 4 stroke outboard recently restored. It came with the boat with no way to mount it. As mentioned in previous threads by myself there is a Volvo Penta 2003 model 28 Hp Diesel inboard with a sure drive. The vessel has a stern tube, propshaft, new cutlass and stave bearings, and fixed blade propeller. 17 X 12 LH.

The dilemma is to decide what to do. and I have been taking opinions. One 'expert' says fit both. and use the outboard to leave the marina. Then fire the diesel at full revs once out at sea if there is no wind: because the inboard will vibrate a shake a lot at low revolutions. I actually have a couple of more votes for both... one person does not trust diesels & prefers gasoline engines. Another view is that there is a lot of water weed close in to shore and the outboard prop may be easier to clear. + The outboard could be a good kicker for fishing.

The inboard only votes are that the diesel is more reliable in rough weather. and leaving the outboard off the boat allows buoyancy capacity for 115 lbs of more fuel. Coastguard and insurance do not like Gasoline fuel on boats.

The votes for blanking off the propshaft and going with outboard only. Are more room in the interior for storage and less smell of fuel. lighter weight for sailing.

So my question is do any of you have your sailing vessel set up with both options??
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Old 07-12-2016, 15:13   #102
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Re: Inboard vs. Outboard for Cruising

We have a friend who fitted an outboard bracket onto the scoop of his heavy (10 tonnes) cruiser. His OB is a 25hp Yama.

So he added an outboard ability to an existing inboard facility. He tested this in flat water and it worked very well.

He went out and sailed his rtw. He never used the optional extra. But it was there, just in case.

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Old 07-12-2016, 15:24   #103
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Re: Inboard vs. Outboard for Cruising

Before boat choice changed I was going to buy a boat with an inboard and then add an outboard bracket that the dinghy motor of 6-8 hp could be mounted on to push the mothership on as a back up. Also I was going to get an electrical motor and extra solar panels so I could push the mothership with that too.
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Old 07-12-2016, 15:27   #104
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Re: Inboard vs. Outboard for Cruising

Coastalexplorer, is your boat a Ricard Carlson design?
Re the motors, you said a "a sure drive". I'm guessing you didn't mean 'saildrive'. Personally my preference for saildrives is pretty low, corrosion and membrane replacement dramas.
But if it were mine and it was going to be a shaft drive then the decision is easy.
I can see your pro's and con's...very hard decision.
But having had an outboard hanging off the back on a previous boat, a Sailmaster ultra long shaft, my leaning is toward the Volvo because you are guarranteed to always have the prop in the water when the seas are rough but the wind has died.
Other thing, with the outboard, really hard to reach the controls and a small tank in the cockpit.
For what it's worth.
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Old 07-12-2016, 16:22   #105
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Re: Inboard vs. Outboard for Cruising

Coastal's question was whether anybody had both an inboard and an outboard mounted.

To me the starting point to this question is whether you would have that outboard on your dinghy and if not that outboard then would you want a bigger or smaller outboard or none at all?

For Coastal: assuming 24'lwl, 11,000lb loaded, 25lb thrust per HP and using Skene's graph:

9.9 hp in flat water should push you 6.0-6.75kt so it should be plenty in light to moderate conditions.

6 hp in flat water should push you 5.5-6.25kt so it would be fine in calm to light conditions.

5hp in flat water should push you 5.25-6.0kt so it would be fine in calm to light conditions.

3.5hp in flat water should push you 4.75-5.5kt so it would be fine in calm conditions.

As a backup motor any of these would be adequate although some would be more adequate than others. You might consider using an 8 or a 9 hp as a prime mover but I wouldn't go below that and you would have to live with not being able to use the motor in rough conditions unless you created a motor well forward of the stern. A question you need to ask yourself is how often do you run into rough conditions with no wind.
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