Inboard vs. Outboard for Cruising

[newhaul]

Originally Posted by kmacdonald

My Capri 22 got 17 mpg with a 3.5 HP two stroke at 4.5 kts. It gets 20 mpg with a 4 HP Tohatsu four stroke at 4.5 kts. These are real measured numbers, not guesses.
The 4 HP will push it into strong wind and waves but the 3.5 HP would not. High thrust prop on the 4 HP makes a big difference.

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.

[yalnud]

Originally Posted by newhaul

One thing I have not seen listed. My 8 HP outboard is also the motor for my tender so I don't have extra weight of an additional engine .

Is it a long shaft? If so how do you find performance on your tender versus a regular shaft. I have a long shaft 6hp on my tender and i find i get cavitation from it.

[newhaul]

Originally Posted by SailingFan

Well, to chime in on this one, I have an inboard Yanmar (8 hp) and an outboard Evinrude (8 HP also, but with slightly smaller prop, just barely). Both props have three blades. The sailboat prop is non-feathering.

Now, the Yanmar was not running when I bought the boat, I assumed it was dead and that I would have to remedy the situation at some date in the future by either fixing it or removing it for the additional storage space that removal would provide. The outboard is exceptional for a 2-stroke and as a long shaft design its prop is about precisely the same depth as that of the inboards blades. I used the outboard exclusively on my trip up the ICW from Daytona, and it did not fail me, not once. However...

There were multiple occasions when there was cavitation when I was dealing with wakes of other vessels. I can imagine that in open water with chop the outboard would quickly become rather cumbersome, but I also can honestly state the boat will turn in her length, pivoting on the keel, in a tight space, and that is by far an excellent situation, given how tight the St. Augustine marina was for us to navigate (in high winds, with contrary currents with the tidal flow as we wound through a maze of mega-dollar yachts that cost more than any house I have ever set foot in, to include some pretty schmantzy houses).

The outboard was quite valuable and effective, though it did go through some fuel. I cannot state how the inboard compares in effective horsepower though, because my three inch fouled hull still hit 5 plus knots with the outboard, and I am unsure if the inboard would have given more considering the state of hull fouling we had for the trip. I will repost later when that is evaluated, after she is back in the water again. My theoretical hull speed is under 7 knots, so I doubt the inboard would have given me much more than the outboard did in terms of speed.

The outboard was noisy. The inboard would likely be noisy as well, but I don't know how noisy it would be. Again, it was not running, and I only recently have gotten the cause of it's silence addressed, and am only now ready to bleed the system and attempt a start. I may do it Tuesday this week, in fact. We shall see.

I can also state that the outboard performed excellent second duty as a launch engine, but the long shaft made it a little tricky on ramps because of the increased depth, and also made it a bit difficult to steer the launch because of the geometry of force that long shaft offered in turns on a flat bottomed launch, and the horsepower was not terribly high, so the launch was almost planed but not quite, and would side-slip in turns easily. Still, beats swimmin' in gator infested waters!

I think I agree with the one that mentioned that the outboard was a good backup for the inboard which was itself a good backup for the sails on a sailboat. That seems to be a reasonable evaluation and represents my own experience in this process. If I had an oar or two on board, I would be even happier, but I do have a galvanized ten foot long pole for poling off of docks and the like, so I suppose that will have to do for now. I don't have tons of room anyway, but the thought of pulling the inboard and selling it off so I can make better use of the space it currently occupies keeps entering my mind, until I consider how much "fun" would be experienced in choppy water along a stone jetty with an outboard that was cavitating in the lumpy soup.

I really need to get that Yanmar running....

Looking forward to your report on economy and performance with the Yanmar running. You did a beautiful writeup on the outboards performance.

[newhaul]

Originally Posted by yalnud

Is it a long shaft? If so how do you find performance on your tender versus a regular shaft. I have a long shaft 6hp on my tender and i find i get cavitation from it.

Yes it is a tohatsu 2 stroke 8 HP sail drive outboard . I dont have any cab issues on the tender.I also don't go fast don't have a need to.
Don't have cavitation issues on my islander either until I am fighting thru 4 to 5 ft following waves with less than a 5 or 6 second dominate period.

[thomm225]

Originally Posted by kmacdonald

My Capri 22 got 17 mpg with a 3.5 HP two stroke at 4.5 kts. It gets 20 mpg with a 4 HP Tohatsu four stroke at 4.5 kts. These are real measured numbers, not guesses.
The 4 HP will push it into strong wind and waves but the 3.5 HP would not. High thrust prop on the 4 HP makes a big difference.

It's a big help that your boat only displaces 2200 lbs

My 5 hp is pushing a 6600 lb displacement boat and I can still motor across the 20 miles of the lower bay with a little over a gallon of gas...........wind, waves, and tide depending

[newhaul]

Originally Posted by thomm225

It's a big help that your boat only displaces 2200 lbs

My 5 hp is pushing a 6600 lb displacement boat and I can still motor across the 20 miles of the lower bay with a little over a gallon of gas...........wind, waves, and tide depending

Actually the weight of his vessel means nothing in this case he is reporting the difference between a two stroke outboard and a similar sized four stroke outboard on his vessel. So those are good numbers to look at.
( I bet the economy difference can be attributed to the high thrust prop alone. JMO)

[newhaul]

Originally Posted by thomm225

It's a big help that your boat only displaces 2200 lbs

My 5 hp is pushing a 6600 lb displacement boat and I can still motor across the 20 miles of the lower bay with a little over a gallon of gas...........wind, waves, and tide depending

Sorry tom but I actually find that hard to believe .
Your 5 HP has to be running at near full throttle to push your boat to its 6.5 knot hull speed and it would take just over three hours to cross the 20 miles . That's even better economy than I would expect out of a diesel inboard or outboard.

[thomm225]

Originally Posted by newhaul

Sorry tom but I actually find that hard to believe .
Your 5 HP has to be running at near full throttle to push your boat to its 6.5 knot hull speed and it would take just over three hours to cross the 20 miles . That's even better economy than I would expect out of a diesel inboard or outboard.

I very rarely run it at full throttle. I usually have it at 1/2 to 2/3 because it really doesn't help much after that.

As best I can figure it's a bit over a gallon (in the right conditions) and it takes me anywhere from 3 hours to 5 hours at 3-7 knots depending on wind, waves, tide, and whether or not I can motor sail. I believe the stats on the engine say it will run at full throttle for 50 minutes on the 40 ounce integral tank.

Here is one of the few times I maxed it out. The tide is running so hard the pilings for the fish nets are moving back and forth 6"- 1'. I wish the video was better but maybe you can see the current in the water

Max speed I could get was about 2.7 knots.

The fish nets are in about 4-5' of water and I'm in 35'. Ocean is about a mile or so to my stern and I'm headed toward the cement ships at Kiptopeke

https://www.youtube.com/watch?v=q6sHpweobRM

[Adelie]

Originally Posted by newhaul

Sorry tom but I actually find that hard to believe .

Your 5 HP has to be running at near full throttle to push your boat to its 6.5 knot hull speed and it would take just over three hours to cross the 20 miles . That's even better economy than I would expect out of a diesel inboard or outboard.

He didn't indicate he gone hull speed, he just indicated he'd done 20miles on a little over 1 gal of gas.

At 4.5kt that wouldn't be at all surprising. At 4kt I'd be a little surprised he wasn't under 1gal.

[boatsail]

One thing I have not seen on here is the stink of the diesel. I have a cal 2-27 with 6hp ob. I really like it. Take it home in winter service, get it running fresh and take it out in spring. sure here are a few annoyances, but imo, that is all they are. Annoyances. I'm not talking about big boats here, I'm talking about a small 27 foot sailboat that is easy to handle. I avoid the fuel smell inside, the engine stink. I would not want an inboard on any boat small enough to have an outboard. It's that simple. Sure there are always trade offs. I'll end with a story.

I chartered in BVI. Great trip. a bene 36. Nice boat. New, only 2 years old. Professionally maintained. after a week in the boat, when we got home we noticed (did not notice it while on the boat, cause like B.O., you are used to it) that all of our stuff smelled like diesel. I looked at the engine, it was spotless, but its just what engines do, they stink.

personsally, I'm most likely going to have a cat as my next boat and one of the main reasons is that that I can get one with absolute separation of engine and interior. To have an engine in your living room will stink to all those who say it does not, I disagree no matter what you say. My wife has extremely happy with the ob setup and realized the shortcomings, but is happy due to the more livable interior.

[Sidney777]

Well, the first time you have waves lifting the outboard out, or almost out of the water you will know, or at least have an experienced opinion. (Also, you may need a newer outboard that can operate with waves or splashed water coming over the top--and outboard still running)? .....Also, emergency or semi-emergency situations with high waves,wind,rain can be a problem with outboard lifting out of the water. And Many Carburator problems. (Stolen outboards)? --Following seas ? GAS supply.. if you use outboard a lot, you need 20 to 40gal on board if no gas resources. But, electric start outboard easy for inshore work. I had 9.9hp honda on 26ft, 5400lb sailboat & sufficient, But now 15hp is Great, better.

[thomm225]

Originally Posted by newhaul

Sorry tom but I actually find that hard to believe .
Your 5 HP has to be running at near full throttle to push your boat to its 6.5 knot hull speed and it would take just over three hours to cross the 20 miles . That's even better economy than I would expect out of a diesel inboard or outboard.

On top of my explanations above, the fuel amount used is best guess.

I rarely motor the entire distance.

Sometimes I'll sail off anchor or motor off using the integral tank before raising sail. If the wind just won't stay up, I'll restart the engine and switch to the external tank

I'll raise sail again if the wind comes back up. Sometimes I can use a very flat main and get a boost and other times it's the jib depending

Then you have to add in (or subtract) the current, waves , wind, etc

Many times I'm coming down the center of the bay in my neighborhood at 76 10 Longitude so there are lots of variables out there. This lines me up with my creek or at least the Hovercraft Pad nearby

Then there are times when I can sail the whole way back especially if I'm up North a ways on the Western side and have a nice SW wind to work with

[boatsail]

I have found for the most part that when the outboard really sucks I should instead be sailing as a general rule.

[Don C L]

I used a 9.9 long shaft on a RIB once... nearly ripped the transom off ... thrust was way too low

[SailingFan]

Originally Posted by boatsail

I have found for the most part that when the outboard really sucks I should instead be sailing as a general rule.

This is the part that I have been considering as well, quite often. The only snag is that the poor weather may be happening where there is little sea room and a bit of shipping traffic, and then the engine would really be handy (and because of the cavitation in wakes issue, not useful after all). Therefore I had resolved to either fix the inboard to have all three options for propulsion, or remove the inboard and hope for the best with sail use. Either way, though, I will be working on refining sailing techniques to minimize the chances that the outboard is the only thing between me and a stone jetty, such as those structures near Mayport and St. Augustine, Florida. There is some great fishing and sailing to be had in those areas, but the jetties can absolutely EAT a powerless sailboat in mere minutes due to the blocky nature of the boulders there.