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Old 26-03-2020, 21:31   #1
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Inboard diesels vs 2 stroke outboards.

Hi,
I want to build a plywood boat 5 meter-ish however I'm in love with the concept of inboard diesels due to other non existent passion fast cars.

But the reality is i can get a modern 2 stroke petrol outboard and place it off the rear or in a well and get around just as well.

However since i live in Darwin Australia there's thousands and thousands of kilometres of largely inhabited bush and islands out there to explore and fish so I'm thinking the extra expense of getting even an Ebay 10hp single cylinder diesel and drive shaft prop etc is more reliable and cheaper on the fuel than the outboard will ever be, until i can graduate to a bigger boat and attempt to be a real sailor.

Am i being stupid ultimately, or have i valid point. That said i have the passion but not the finances hence cheep cheep.
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Old 26-03-2020, 22:43   #2
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Re: Inboard diesels vs 2 stroke outboards.

Make sure you can get the right prop for the boat for your outboard if you choose that route.

With a modern, fuel injected outboard, your fuel burn will still be higher but not shockingly so.

Get whatever you're happiest with, really. Outboard is significantly easier to install and replace. Diesel should last longer.
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Old 27-03-2020, 01:52   #3
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Re: Inboard diesels vs 2 stroke outboards.

A 5 metre boat with a diesel would be rare indeed. I'd not chance a diesel of questionable quality, if you're travelling off the beaten path. Then there's the shaft, stuffing box, p bracket and rudder. It will be quite a bit more fuss, on a 5 metre boat, to use a diesel.

A no name diesel is not what you want in the "bush". A yanmar or other well known brand, would be fine. But on a 5 metre boat, on a tight budget... Maybe not the best idea.

Definitely go with the outboard, no question. They're cheap, light, and easy to maintain.

Cheers, and happy exploring.
Paul.
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Old 27-03-2020, 02:01   #4
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Re: Inboard diesels vs 2 stroke outboards.

Having seen hudreds of dnghiies, when long distance sailing, all had petrol outboards.
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Old 27-03-2020, 04:00   #5
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Re: Inboard diesels vs 2 stroke outboards.

I would go with a 4 stroke outboard...preferably fuel injected (assuming available in the size range you want).

Unless you are getting a used diesel on the cheap, an outboard will be so much cheaper you will never make it up in fuel savings.

We had a 25hp 4 stroke EFI outboard on our 10m catamaran. The boat had sister ships with diesel and they only got marginally better fuel economy.

One advantage to an outboard is you can pull it completely clear of the water, so no growth or corrosion issues to worry about.
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Old 27-03-2020, 05:17   #6
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Re: Inboard diesels vs 2 stroke outboards.

A 5m boat would also benefit from a pair of sturdy oars.
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Old 27-03-2020, 05:37   #7
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Re: Inboard diesels vs 2 stroke outboards.

I guess I just see the fun in the diesel. Picturing like a small diesel launch.
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Old 27-03-2020, 06:55   #8
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Re: Inboard diesels vs 2 stroke outboards.

Quote:
Originally Posted by Rufus McDuff View Post
Am i being stupid ultimately, or have i valid point.

I don't think you have a valid point.


9.9 hp outboards are inexpensive, reliable, abundant, lightweight, and easy to repair. 2 stroke, 4 stroke, carb, fuel injection, it doesn't really matter much. They can be readily removed from the boat making the boat easier to trailer and the outboard easier to service.


In these sizes you might consider an inboard if you are building a boat with a narrow stern or a pointed stern that doesn't have the space or the stern flotation to accommodate an outboard. There are some tunnel hull designs out there that do this, that are extremely shallow draft. Most use a rotax gasoline (petrol) inboard, because they are light.



Quote:
That said i have the passion but not the finances hence cheep cheep.
Outboard is going to be considerably cheaper. Around here you can get used ones from a dealer, with a warranty, for as little as (US$) $500, and new ones for around $2500.



Oars are cheaper still.
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Old 27-03-2020, 08:06   #9
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Re: Inboard diesels vs 2 stroke outboards.

I’d vote outboard too. Cheaper in the long run, easier to maintain and service.
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Old 27-03-2020, 08:13   #10
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Re: Inboard diesels vs 2 stroke outboards.

I would go with outboard and maybe buy a spare as well. However, diesel is far safer than gas so pay attention to your storage set up.
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Old 27-03-2020, 08:17   #11
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Re: Inboard diesels vs 2 stroke outboards.

Hi Rufus, so much goes into the mix when considering the diesel. Exhaust elbow, muffler, starter, battery, oil & filter changes, fuel tank and assorted filters.

I would go for a good, reliable 2-stroke to avoid the 4-stroke filter and oil changes. Keep it as simple as you can and you will enjoy you boat more. Oh, 2-strokes also have more torque (pulling/pushing power) than the 4-strokes!

Now please excuse me as I have to do an oil and filter change this morning. Grrr
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Old 27-03-2020, 08:32   #12
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Re: Inboard diesels vs 2 stroke outboards.

Remember the movie "The African Queen".
Perfect boat.
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Old 27-03-2020, 08:49   #13
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Re: Inboard diesels vs 2 stroke outboards.

For exploring backwaters etc in that size boat go with an outboard. You can tilt up and get into some tight places etc.
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Old 27-03-2020, 09:12   #14
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Re: Inboard diesels vs 2 stroke outboards.

McDuff:

Quote: “I want to build a plywood boat 5 meter-ish...”

A couple of things to add to your considerations: A five metre long boat is the size of a sailing dinghy. It will not like to carry the weight of a diesel engine with all the associated clobber like sterngear. Doing so would, IMO, confine your top speed to “hull speed” which would mean five or six knots. You are in Darwin with miles and miles of water to explore, you say At 6 knots? Not really viable, in my opinion.

Now as a dinghy, under sail, if you have any kind of wind, twice that speed is perfectly feasible. If there is no wind you can row effortlessly for hours on end at, say, 3 knots, and in silence. With a light outboard you'll be able to get 10 or 12 knots. But carrying enough fuel for a long voyage would be a problem.

But even at those speeds, exploring miles and miles will take ages. There are people that undertake quite long voyages in sailing dinghies. Some have taken dinghies all around Scotland in the open sea. So you might like to think about that for a bit. Look up “Wayfarer dinghy” on Google for some ideas.

All the best,

TrentePieds
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Old 27-03-2020, 09:43   #15
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Re: Inboard diesels vs 2 stroke outboards.

Quote:
Originally Posted by TrentePieds View Post
McDuff:

Quote: “I want to build a plywood boat 5 meter-ish...”

A couple of things to add to your considerations: A five metre long boat is the size of a sailing dinghy. It will not like to carry the weight of a diesel engine with all the associated clobber like sterngear. Doing so would, IMO, confine your top speed to “hull speed” which would mean five or six knots. You are in Darwin with miles and miles of water to explore, you say At 6 knots? Not really viable, in my opinion.

Now as a dinghy, under sail, if you have any kind of wind, twice that speed is perfectly feasible. If there is no wind you can row effortlessly for hours on end at, say, 3 knots, and in silence. With a light outboard you'll be able to get 10 or 12 knots. But carrying enough fuel for a long voyage would be a problem.

But even at those speeds, exploring miles and miles will take ages. There are people that undertake quite long voyages in sailing dinghies. Some have taken dinghies all around Scotland in the open sea. So you might like to think about that for a bit. Look up “Wayfarer dinghy” on Google for some ideas.

All the best,

TrentePieds
Nah, there are plenty of 16-17 foot boats out there with V8 gas engines... but point taken. Doesn't make a lot of sense.
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