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Old 08-12-2016, 09:44   #121
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by newhaul View Post
Sorry to break it to you but here are a couple things you really should consider.
First real world trumps those graphs and formula every time.
Second what is flat water . Just because there is no wind or discernible waves. Does not mean there is no current you have to work thru.
I had a 6 HP evinrude on my boat. It was barely enough now I have an 8 HP ( both are 2 stroke) there have been times that I was wanting more power.
I'm sorry, I must have given you the impression that I'm stupid. My mistake. Please be advised that I am not stupid.

Please also note that the recent focus of this thread is the use of an outboard as a backup to an inboard, not as the prime mover after sails.
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Old 08-12-2016, 11:06   #122
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Re: Inboard vs. Outboard for Cruising

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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.
A couple more data points as I left them out of the original. You are right that lwl is 24' loaded for my boat and 9200 lbs loaded is remarkably close to what I estimated her at loaded! My lwl of 24' gives a 6.56 knot hull speed. Neither of the motors on my boat ever got me there. The 6 HP sailpro gets me to 5, and the diesel got me to 5.5. It must be all the bottom paint! These numbers are comparable (both flat water with no current or wind). Not being familiar with the skene graphs and not being able to find a curve online, I'm not sure what they would say about where these numbers position me on the curve regarding diminishing returns to power. But, I'd imagine I'm still short of trying to climb the bow wave, which is where I would think the greatest inefficiency comes in. So I don't believe the diesel would have performed better motoring into wind or waves, except from a not being torn out of the water perspective, as its benefit was minimal under ideal conditions with it giving me a maximum speed short of hull speed - I.e. there was nothing left in reserve power, and nothing being wasted trying to climb the bow wave.

My point being, I honestly don't think, that given how diesels are generally installed and the aged nature of them on older boats, that they are a superior choice to outboards on older boats, unless you need the ability to reverse strongly, don't like getting slapped around by waves when the wind dies but the waves remain, really hate gasoline, or plan to motor vs sail in less than ideal conditions. So I think the choice would come down not to efficiency, which in my experience would seem to indicate a near wash, but more subjective criteria.

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Old 08-12-2016, 11:35   #123
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Re: Inboard vs. Outboard for Cruising

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Thomm as a fellow single hander I have two words to make it a lot easier " lazy jacks"
Maybe one day, but for now I have found that wrasslin' with the mainsail during take down (and tie off) while trying to steer, start the engine, not spill my beer, readjust the topping lift while avoiding other boaters does provide a decent end of the sail day workout .....especially when it's rough.

And btw, I have to go to the mast to lower the main ..................

On other days, I'll leave the jib up and the autopilot engaged and just lower the main without a lot of drama. Then tie off, readjust the topping lift, lower the engine, start the engine, position and tie off the engine, put it in gear, set throttle, then furl up the jib

I was a bit ahead of the takedown game in the video below and only about 5 miles out and just one more shipping channel to cross when the cloudline passed over bring the wind back up. So I brought the jib back out for a bit more speed. It's different coming in every time it seems

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Old 08-12-2016, 13:34   #124
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Re: Inboard vs. Outboard for Cruising

We installed lazy jacks, then took them down because they got in the way. I don't see an advantage to having lazy jacks on a small boat. Being able to reef without changing course or sail trim is a huge advantage, and lazy jacks seem to clutter the process.

Brian
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Old 08-12-2016, 15:20   #125
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by DawnTreader View Post
We installed lazy jacks, then took them down because they got in the way. I don't see an advantage to having lazy jacks on a small boat. Being able to reef without changing course or sail trim is a huge advantage, and lazy jacks seem to clutter the process.

Brian
Brian if jacks made things worse for you I would have to say they were likely not installed right for your vessel and sailing style either that or they were not designed for your exact vessel. I design and install jacks in boats from 22 to 42 ft and have never had any issues.
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Old 08-12-2016, 15:24   #126
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by Adelie View Post
I'm sorry, I must have given you the impression that I'm stupid. My mistake. Please be advised that I am not stupid.

Please also note that the recent focus of this thread is the use of an outboard as a backup to an inboard, not as the prime mover after sails.
Adelie I never thought any such thing I am sorry if I offended you.
You kept quoting some rather archaic formulas I was just pointing out the fact that real world always trumps the engineers office formulas.
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Old 08-12-2016, 15:26   #127
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by thomm225 View Post
Maybe one day, but for now I have found that wrasslin' with the mainsail during take down (and tie off) while trying to steer, start the engine, not spill my beer, readjust the topping lift while avoiding other boaters does provide a decent end of the sail day workout .....especially when it's rough.

And btw, I have to go to the mast to lower the main ..................

On other days, I'll leave the jib up and the autopilot engaged and just lower the main without a lot of drama. Then tie off, readjust the topping lift, lower the engine, start the engine, position and tie off the engine, put it in gear, set throttle, then furl up the jib

I was a bit ahead of the takedown game in the video below and only about 5 miles out and just one more shipping channel to cross when the cloudline passed over bring the wind back up. So I brought the jib back out for a bit more speed. It's different coming in every time it seems

Didn't realise you had furling on jib. That would make things even simpler for me.
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Old 08-12-2016, 17:07   #128
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Re: Inboard vs. Outboard for Cruising

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Originally Posted by DawnTreader View Post
We installed lazy jacks, then took them down because they got in the way. I don't see an advantage to having lazy jacks on a small boat. Being able to reef without changing course or sail trim is a huge advantage, and lazy jacks seem to clutter the process.

Brian
Yep, that's pretty much why I haven't installed them either

Plus I have a floating gooseneck........../boom
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Old 08-12-2016, 18:14   #129
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Re: Inboard vs. Outboard for Cruising

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I was just pointing out the fact that real world always trumps the engineers office formulas.

Where do you come up with this stuff?

This engine and this plane were built by engineers based on their office formulas. Both did pretty well in the real world in 1940

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Old 08-12-2016, 18:25   #130
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Re: Inboard vs. Outboard for Cruising

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Where do you come up with this stuff?
There are a great many engineering successes.

And then there was the Tacoma Narrows bridge...

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Old 08-12-2016, 18:25   #131
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Re: Inboard vs. Outboard for Cruising

Thomm it was actually a field mechanic/engineer that suggested adding a supercharger to the merlin engine which made it as great a success as it was. But yes the rolls merlin was an awesome engine for fighter aircraft when they added the supercharger.
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Old 08-12-2016, 18:29   #132
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Re: Inboard vs. Outboard for Cruising

Good engineers recognize the unknowns and latent assumptions of their office work. Great ones observe unknowns affecting their work bin the real world and get a modulus/equation/method named after them.
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Old 08-12-2016, 18:31   #133
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Re: Inboard vs. Outboard for Cruising

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Thomm it was actually a field mechanic/engineer that suggested adding a supercharger to the merlin engine which made it as great a success as it was. But yes the rolls merlin was an awesome engine for fighter aircraft when they added the supercharger.
And yes, Mitchell's designed of the Spitfire going totally against the thinking of the times was the main point I was making above.....

But I do like the Merlin engine sound........

and as far as the mechanic suggesting the supercharger, that's like someone coming up and finishing the last two words of a crossword puzzle after someone else has filled in the first 50 words or so
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Old 08-12-2016, 18:56   #134
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Re: Inboard vs. Outboard for Cruising

...a supercharged outboard?... I like it!
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Old 08-12-2016, 19:00   #135
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Re: Inboard vs. Outboard for Cruising

Thomm I will conciede that point about the spitfire . Yes the merlin is a wonderful sounding engine saw and heard many many in my youth in unlimited hydroplanes .
Back to the topic now.
I noticed in your last video there was a good following sea but I didn't hear any change in the sound of your merc. outboard. Prop never left the water.
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