Thread: Petrol or Diesel for boats

Initial purchase cost is one of the biggest drivers when buying boats and that extends to the motor. For packing and power to weight the two stroke outboard has been the go. As time goes on two strokes are being limited as to where they can be used with some fresh water lakes O/S ruling the two strokes out and having to use four stroke outboards. It is a pollution issue.

Diesels much more expensive to buy initially but probably pay for themselves in fuel and maintenance costs.

Plenty of planing hulls get around with diesel stern drives. I used to see a Volvo penta driven boat at the ramp we used to go in off.

In terms of ski boats outboards will keep you poor, an inboard marinised V8 will give you a days skiing for the same juice a two stroke outboard would give you an hour.

I don't know that I would get a diesel for a ski boat but a cruiser/fishing boat, if I could afford it I would go the diesel stern drive.

Thanks for this 'roverrescue', much appreciated.

Is there much difference in servicing cost/intervals 'tween diesel inboard and a petrol outboard?

I run a Holden V8 inboard in my ski boat.

There is a certain procedure that I follow before even starting it. It it travels with the covers on, then they are taken off, and the motor cover lifted for 10 - 15 mins before I connect the battery.

Before the battery is connected, double check that all switches are off, so that there is nothing to draw a current, and possibly cause a spark.

I have also installed 2 bilge blowers. 1 sucks in fresh air from one side, and the other expells air out the other side. These are run for about 10 mins or so while we are getting things arranged, & backing the boat into the water.

I will leave them running for another 15 mins or so after setting off.

I have also replaced all the fuel lines etc, and double check everything before we leave home.

As an ex-firefighter, I am pedantic about the checks, and will never have anyone else onboard when I start up.

Re-fuelling is done when everything is cold. Usually, we will do it after lunch, and then leave the motor cover open for a while again before starting.


The whole point is, that while petrol is more explosive than diesel, if treated properly, & with a bit of common sense, then it can be safe.

Which is better for the particular application? I have no experience with a diesel in a small boat, but in a big heavy boat, like a cruiser or tender, then I would go diesel all the way.

Originally Posted by Basil135

I run a Holden V8 inboard in my ski boat.

There is a certain procedure that I follow before even starting it. It it travels with the covers on, then they are taken off, and the motor cover lifted for 10 - 15 mins before I connect the battery.

Before the battery is connected, double check that all switches are off, so that there is nothing to draw a current, and possibly cause a spark.

I have also installed 2 bilge blowers. 1 sucks in fresh air from one side, and the other expells air out the other side. These are run for about 10 mins or so while we are getting things arranged, & backing the boat into the water.

I will leave them running for another 15 mins or so after setting off.

I have also replaced all the fuel lines etc, and double check everything before we leave home.

As an ex-firefighter, I am pedantic about the checks, and will never have anyone else onboard when I start up.

Re-fuelling is done when everything is cold. Usually, we will do it after lunch, and then leave the motor cover open for a while again before starting.


The whole point is, that while petrol is more explosive than diesel, if treated properly, & with a bit of common sense, then it can be safe.

Which is better for the particular application? I have no experience with a diesel in a small boat, but in a big heavy boat, like a cruiser or tender, then I would go diesel all the way.

GREAT POST!!!!
Its why you are still with us.
Andrew

Originally Posted by big guy

If its a small boat, I would definately go for a new 4 stroke, they produce great torque, good top speed and low in service costs.

They now use half the fuel of old 2 strokes, on my old Markham whaler, i pulled two 70hp outboards off and replaced with two 50hp four strokes, much better hole shot, doubled the economy and are dead quiet.

So long as you have proper tanks, venting and filters you should be fine.

Exotic complicated in boards are great but make sure you find a good service centre and resale is another thing.

If not a Z drive can be hard to beach and they do take up a fair bit deck space.
happy boating.

Interesting this. We replaced the motor on our boat at work last year.

Previous motor Honda 90HP 4 stroke.

New motor Evinrude Ecotech 90HP 2 Stroke.

There is no comparison, the 2 stroke is smaller, lighter and has better torque characteristics than the 4 stroke, is quieter and more economical. Plus with it's long service intervals, it's an all round winner.

Originally Posted by LandyAndy

Petrol outboards are a totaly different explosion risk.The engine hangs off the back of the boat,inboards are under the floor,leaking fuel into the bilge,one spark,kaboom.There are atmosphere sniffer alarms on most modern inboards to warn of fuel fumes.
Andrew

Hi Andy, need to remember that most 20 foot + boats have underfloor fuel tanks, seen some horror stories where these have split.
cheers
blaze

What happened to the Yanmar diesel outboards. They seem to be no longer available???

Originally Posted by numpty

Interesting this. We replaced the motor on our boat at work last year.

Previous motor Honda 90HP 4 stroke.

New motor Evinrude Ecotech 90HP 2 Stroke.

There is no comparison, the 2 stroke is smaller, lighter and has better torque characteristics than the 4 stroke, is quieter and more economical. Plus with it's long service intervals, it's an all round winner.

Was the honda old school 4 stroke?

The new era are just brilliant. I do believe much works has been done to improve 2 strokers also and they performance is outstanding.

So improvements all round I guess.
I am only quoting from real life experience.

As a whole , I believe service intervals have been greatly improved on all out boards now.
I always remembered that after a service they ran like crap and only after some tinkering did I have my old faithfuls back.

A Yanmar or Volvo inboard diesel would probably solve all those issues.