Motor Boat Drive Choice

[Falmouth Flier]

So I am sure that this has been asked millions of times before, but I'm hoping that the experience out there can help.
Currently looking at buying a used motor boat circa 24ft, will primarily be used for coastal cruising & fishing around the Cornish & Devon coast but would still like a bit of performance.
Of the 3 boats in the frame 1 has an outboard, 1 has a petrol Volvo inboard + Stern Drive & 1 has a diesel Volvo inboard + shaft.
I have heard masses of stories about Stern Drives being hideously expensive to maintain compared to an outboard or shaft drive setup.

Any advice or guidance please ?

 

[julians]

assuming all boats are identical except for engine and drive type, my order of preference would be as follows :-

1. outboard
2. diesel inboard + shaft
3. diesel inboard + outdrive (I know it wasnt on your list, but I put it here to illustrate where I'd place the different types)
3. petrol inboard + outdrive


Depending on how many hours I was doing, I may swap 1 & 2 around - also the availability of petrol where you boat might sway a decision as well (its very available where I boat, but may not be where you boat)

I suspect however that there will be more differentiating attributes than just engine & drive type, ie price, age, condition, spec, actual engine model and power , fuel availability etc etc. ie I wouldnt buy an ancient boat just because it has a diesel and shafts. And I wouldnt just buy a boat with an outboard if I felt it was going to be underpowered etc etc

Everything is a compromise with boats - choose your compromise.

stern drives probably are more expensive to maintain on average over the long run than shafts or outboards, they're certainly more complicated and can give you a big bill (but so can anything boaty) . But they're more fuel efficient than the same engine on a shaft.

Outboards are more simple, but petrol is not the most efficient way of moving a boat.

Shafts are very simple, but relatively fuel inefficient.

Diesel gives better fuel economy and is available in a lot of places along the coast in the UK. but diesel boats tend to be more expensive than an equivalent petrol boat to buy.

petrol has worse fuel economy , and is not as available as diesel in the uk, but the boat will probably be cheaper than a diesel boat to buy

blah blah blah

 

[Portofino]

Diesel inboard + shaft will be most economical going Fwds . More saleable at the end .
What diesel marque is it btw ?

Petrol + boats if you can choose which is your situation is best avoided .

 

[Ian h]

where would people place Diesel outboards ? Or is it too early in their evolution to make informed comments

 

[GrahamHR]

where would people place Diesel outboards ? Or is it too early in their evolution to make informed comments

We had VP 5.7 V8 petrol/ outdrive boats frrom 2001 to 2013. Easy to maintain, fast, smooth. No issues at all. .....................................Then we had a VP D4-300.

 

[Bouba]

Outboard all the way...even if petrol was scarce, I would choose an outboard over a stern drive...a good outboard, like a Honda, is ridiculously reliable...the only downside is that it can be stolen...so make sure it’s well insured.
Ok... I admit that I didn’t read the question as thoroughly as I should’ve...and I failed to see the diesel on shaft....this is most interesting on a small boat....if I could get the diesel engine checked out AND petrol is hard to find in your location...I just might choose this....but if you keep the boat for a long time and your motor proves unreliable enough to get an engine swap you will wish you had an outboard...choose any size from any manufacturer, possibly get two...outboards are just so flexible

 

[Momac]

Diesel all day long for me as petrol at the waterside is so scarce .

I have sterndrives . The boat is lifted every two years for service and I have had no issues other than a damaged prop on one occasion in the last 8 years .
On the other hand two friends with shaft drive have, in the same period, had expensive transmission failures . So don't be fooled into thinking shaft drive is bullet proof.

 

[KevinV]

Shafts are very simple, but relatively fuel inefficient.

As this forum is a constant learning curve for me, could you explain this please? It seems counter-intuitive, I'd expect much higher transmission losses from a sterndrive (changing the direction of drive twice through 90 degrees, plus some form of cv joint to allow for tilt/ steer), or is this more than offset by shafts having their props not quite parallel to the water flow?

 

[mm42]

where would people place Diesel outboards ? Or is it too early in their evolution to make informed comments

They're not really designed for leisure use, they're very expensive, and very heavy. They're mainly designed for commercial and government / military boats who are committed to doing away with petrol for boats for safety, and because, when used as a daughter craft, they can call on the substantial bunkers of the mother craft.

I don't think we'll be seeing diesel outboards on leisure boats any time soon.

 

[Momac]

As this forum is a constant learning curve for me, could you explain this please? It seems counter-intuitive, I'd expect much higher transmission losses from a sterndrive (changing the direction of drive twice through 90 degrees, plus some form of cv joint to allow for tilt/ steer), or is this more than offset by shafts having their props not quite parallel to the water flow?

In practice sterndrives are certainly more efficient than shaft drive (at fast speeds) in terms of fuel use but I wouldn't let that be a decision factor when buying a boat.

 

[oldgit]

Drilling down.
Suitabilty of the boat for your purposes really ought to be the primary factor in your purchase, no point in buying something that quickly never gets used due to frightening the life out of skipper and crew .
Mechanical condition should be next, better , outdrive boat with an anal previous owner than a diesel on shafts that has never been serviced in its life.
Outdrive/outboard boats tend to be whizzy and get you to your destination quicker but tend to be tippy and less stable at anchor.
Diesels tend to be heavier and more stable, there are of course whizzy boats with deisels, there is price premium on these for a reason.
As boats get older each subsequent owner tends to want / can only afford to spend less and less on essential servicing.
With a diesel on shafts this boils down to oil/filter changes each year and shaft mainatenance every decade.,
With outdrives it is vital that money is spent each and every year to prevent problems and additional money spent every second or third year to prevent different problems.
What previous owners have done becomes more critical as time goes on.

The fly in the ointment .
You will see a totally unsuitable boat with the wrong engines and fall in love with it and all "good advice" /"biased opinion" will fly out the window.
Best to jump in, ignore all the advice and make the mistakes all the rest of us mortals have made and learn the hard way.

 

[julians]

As this forum is a constant learning curve for me, could you explain this please? It seems counter-intuitive, I'd expect much higher transmission losses from a sterndrive (changing the direction of drive twice through 90 degrees, plus some form of cv joint to allow for tilt/ steer), or is this more than offset by shafts having their props not quite parallel to the water flow?

its to do with a couple of factors:-

1. The angle of thrust. Shafts dont run parallel to the water surface, they come out of the hull at an angle, so some thrust is wasted. Outdrives can vary their angle of thrust and keep the direction of thrust parallel to the water surface regardless of speed.
2. Drag. Shafts have the shaft, p bracket and rudder all in the water causing drag. Outdrives just have the fairly hydrodynamic lower casing in the water.

I think the fuel efficiency angle really only comes into play on planing boats - dont think displacement boats have a significant difference in fuel economy . And as mentioned above, fuel efficiency differences between drive systems probably isnt something worth worrying about in the grand scheme of boat running costs

 

[Plum]

Diesel all day long for me as petrol at the waterside is so scarce .

Agree, unless you will be restricting your usage to an area with good petrol supply. In some parts of the country waterside petrol is almost non-existent.

www.solocoastalsailing.co.uk

 

[julians]

where would people place Diesel outboards ? Or is it too early in their evolution to make informed comments

They're not mainstream enough for me yet - a bit too bleeding edge for risk averse me , but I think if they become popular and as a result cheaper, they could be the best of all worlds.

There was someone on the axopar facebook group who had just bought a brand new 37 and fitted it with twin diesel outboards from oxe (OXE Marine ) , the more usual engine choice is twin 300hp mercury petrols. He had a failure of some component on the engine (cant remember what failed) on his first trip out, and oxe couldnt supply a replacement for ages, it didnt sound ideal. Having said that mercury are having supply problems too - I think everyone is right now.

 

[simonfraser]

Coastal cruising, if a few hours per outing it’s easy to bring the petrol in
use a siphon to fill up
outboards are the least hassle

 

[ChromeDome]

.. like a bit of performance ...

Obviously talking planing boats. The performance is a product of the hp available and the ready-to-go GW. Fuel consumption depends on the amount of power you demand from the engine(s). If you call 500 horses to work hard as they can, you need to feed 500 hungry horses.

A benefit with outboards is access when servicing. Remove the cowling and things are just before your eyes. Removal for repair or replacement is bolt-on / bolt-off (hence the risk of theft). Amazingly thieves are able to run away with even very heavy motors.

 

[Commercial Dave]

Diesel all day long for me as petrol at the waterside is so scarce .

Just curious where are you that waterside petrol is scarce? I don't really have much experience outside of my home port but I've been to a few fuel pontoons around here and all of them have petrol. We've never filled our boat from jerry cans

 

[Momac]

Just curious where are you that waterside petrol is scarce? I don't really have much experience outside of my home port but I've been to a few fuel pontoons around here and all of them have petrol. We've never filled our boat from jerry cans

River Trent, Humber and North Sea
There is petrol at Farndon Marina which is our home marina but otherwise nothing unless jerry cans are involved.
While we can get diesel at Hull, Grimsby and our usual destination of Wells Next the Sea.

 

[Plum]

River Trent, Humber and North Sea
There is petrol at Farndon Marina which is our home marina but otherwise nothing unless jerry cans are involved.
While we can get diesel at Hull, Grimsby and our usual destination of Wells Next the Sea.

Anywhere east of the solent and up the eastanglia coast will be a challenge and you will end up having to select destinations based on fuel availability rather than some more interesting ones. It will be like range anxiety with an electric car.

Www.solocoastalsailing.co.uk

 

[oldgit]

Just curious where are you that waterside petrol is scarce? I don't really have much experience outside of my home port but I've been to a few fuel pontoons around here and all of them have petrol. We've never filled our boat from jerry cans

The Medway and Thames Esturary, fuel pontoons with Petrol.

One marina 1 mile above Allington Lock still selling petrol (possibly)
and 20 miles downstream
One marina at Gillingham. (possibly)
Next petrol to the East, Ramsgate (possibly) 60 miles.
Next petrol to the West above Teddington Lock. Shepperton Marina. £2.35 per litre. 70 miles.
Next petrol up the East Coast. Burnham on Crouch.(possibly) .