Petrol to diesel calculations.

[alruss]

My plan is to change to diesel in the next couple of years, my problem is what Bhp diesel
engine do I need to replace petrol engine producing 120 Bhp. I have no idea, but read articles where lower power diesel engines have been used to replace petrol but the boat performance improves. How do I work this out?
Thanks in advance for the useful responses I hope to get.

 

[Bandit]

Firstly ignore the manufacturers fuel consumption figures they are not actual but teoretical.

For realsistic fuel figures Google Honest John the bloke who writes fro the motoring section of the Telegraph his mpg figures are averages of readers actual fuel consumption.

My experience is diesel more efficient in larger engines than smaller.

My sister in law has a golf blue motion which is a 1.6 diesel and pretty efficient.

Rather than say what your current hp figures are now say what your car and cc are and then people can give a realistic proposal.

 

[rafiki_]

My plan is to change to diesel in the next couple of years, my problem is what Bhp diesel
engine do I need to replace petrol engine producing 120 Bhp. I have no idea, but read articles where lower power diesel engines have been used to replace petrol but the boat performance improves. How do I work this out?
Thanks in advance for the useful responses I hope to get.

Diesels, especially turbo diesels produce a lot more torque than equivalent sized petrol engines. So replacing your 120 bhp petrol, you could probably get away with something like an 80-90 bhp turbo diesel, as lont as it produces 30-40% more torque than the old petrol engine. It is torque that you need to accelerate a boat. Pure power is helpful only at the top end. You will note that the diesel will generate peak power and torque at much lower engine revs than the petrol, generally where you need the grunt.

 

[PCUK]

If you want the same level of performance you will need to increase the power of the diesel to overcome the extra weight. It is horse power that decides final performance.

 

[ulyden]

120 bhp is the same. Does not matter whats producing it. Some diesel engines kan keep their horsepower at higher intake temperature, petrol don't.

Some petrol engines don't deliver the rated power.

That some of the reason a 140hp petrol can be replaced by a 120diesel and have more or less same performance.

Most diesels have a consumtion of 0.19 to 0.21l/hp hour Petrol needs 0.3 to 0.32l/h doing the same work.

 

[alruss]

Thanks for the responses, between you, I am now more confused, not that I am complaining mind you.

 

[Bandit]

Sorry **** reply, I thought this was the lounge and you were talking about Cars!

The best way is to say what the boat is and ask if anyone has a diesel version and how it performs.

 

[alruss]

Not much chance of finding a planing diesel version, there were only 40+ made, the diesels were I think single 4108s displacement only, planing were two petrols. She is 40+yrs old Osborne Kingswift. Thanks anyway, you never know. There was another on this forum that was having transit engines fitted, but not posted lately.

 

[BartW]

Diesels, especially turbo diesels produce a lot more torque than equivalent sized petrol engines. So replacing your 120 bhp petrol, you could probably get away with something like an 80-90 bhp turbo diesel, as lont as it produces 30-40% more torque than the old petrol engine. It is torque that you need to accelerate a boat. Pure power is helpful only at the top end. You will note that the diesel will generate peak power and torque at much lower engine revs than the petrol, generally where you need the grunt.

agree,

just to add, you could get away with a less powerfull diesel, but then your max speed will be less.
top speed is depending on max HP,

when you fit same HP diesel like petrol, you will have better accelaration / grunch due to more torque at lower RPM,
and same max speed.

what boat is it ?
as previously remarked, diesel might be more weight, so depending on boat type / weight, might have influence on performance

 

[Tranona]

Not much chance of finding a planing diesel version, there were only 40+ made, the diesels were I think single 4108s displacement only, planing were two petrols. She is 40+yrs old Osborne Kingswift. Thanks anyway, you never know. There was another on this forum that was having transit engines fitted, but not posted lately.

You don't say if it is shaft or outdrive. If the latter you will have to replace the whole package and there are few outdrive packages under 150hp. Although it is possible to marinise vehicle engines at lower cost than new diesels, the current outdrive (if it is one) is unlikely to be able to take the torque. It is rarely economical to replace petrol engines with diesel on old boats as the cost often exceeds the value of the boat and the you would never recoup the costs in fuel savings

 

[MapisM]

the diesels were I think single 4108s displacement only, planing were two petrols. She is 40+yrs old Osborne Kingswift.

I don't know the yard, but I'm very surprised to hear that anyone ever built on the same hull a displacement and a planing boat.
One of those must have been the wrong hull for the job...

 

[Tranona]

I don't know the yard, but I'm very surprised to hear that anyone ever built on the same hull a displacement and a planing boat.
One of those must have been the wrong hull for the job...

Was relatively common in those days when the market was not very big so builders tried to cover the inland waterways displacement market and planing market with one hull. As you suggest not necessarily a good thing, but even now many inland waterways small cruisers use V bottom hulls because of the space it gives - not that many are built nowadays.

 

[Latestarter1]

I don't know the yard, but I'm very surprised to hear that anyone ever built on the same hull a displacement and a planing boat.
One of those must have been the wrong hull for the job...

Never heard of the yard, I am amazed!!!!

One of UK's premier builders of lifeboats and the likes of Blue Leopard http://www.superyachts.com/sail-yacht-2385/blue-leopard.htm

In the 70's William Osbourne built a number of boat on fiberglass hulls, generally with nicely crafted wooden house. All manner of propulsion from 6.354's down to 4.108's. Even featured the BMW gasoline engines and ZF outdrives at one time. William Osbourne never quite got their act together on diesels, they were Morris Marine/BMC engine agents and in the 50's majority of their boats had gasoline motors, latterly moving on to Volvo Penta.

Yes a King Swift can be made to work with diesels, totally feaseable, forget the maths, most certainly impractical.

Also forget marinised Ford Transit engines, this project is totally impractical, however thats boats for you, deserves to be done properly.

 

[neale]

A real life example

When my Bayliner was new with its factory fresh 305 V8 producing 230hp, the brochure top speed was 35mph (it's American so all done in MPH). That equates to a tad over 30 knots.

I replaced the V8 with a four cylinder 170hp Volvo KAD32. Weight wise I think there is probably little between them, the waterline certainly didn't change much.

As well as lower HP, the other significant change was going from a single prop drive to duo prop.

The new top speed with 60hp less was............30 knots.

 

[rib]

ulyden...where do you get your figures from ?

 

[alruss]

Hi, sorry, have not figured out how to do quotes in box.
She has out drives volvo 100 useless over 60hp diesel, I plan to replace with 270s which I have. Was planning to replace petrols with Peugeot 2ltr turbo diesels approx 110hp without any tuning.
As for Osbornes using the same hull for planing and displacement, the planing version starts to lift at approx 7 knots. The displacement hull has fuel tanks and water tanks forward, and only one engine at the stern with out drive, I would think that figure is considerably higher.
The cost hopefully will be kept down because I am going to try and marinise the engines myself, the engines are very common, used by Peugeot and Citroen in many models also, the 8 valve version pretty bullet proof. The boat is not worth what the work will cost but she is Kingswift no1 so I am trying to keep her original outside but petrol is not only volatile and expensive, but very difficult to find. So converting her to diesel is a must really to keep her as a viable vessel.
Many thanks for replies, I feel that what I plan will work well, assuming I can make it work.

 

[JKay]

When my Bayliner was new with its factory fresh 305 V8 producing 230hp, the brochure top speed was 35mph (it's American so all done in MPH). That equates to a tad over 30 knots.

I replaced the V8 with a four cylinder 170hp Volvo KAD32. Weight wise I think there is probbaly little between them, the waterline certainly didn't change much.

As well as lower HP, the other significant change was going from a single prop drive to duo prop.

The new top speed with 60hp less was............30 knots.

with the same original engines and the same swop to the KAD 32's the results were the same for a couple of Fairline Carrera's so it would confirm the efficientcy of modern diesels

forumite "Leomagill" has marinised and fitted a couple of pugs to his mighty vessel and if you follow his link below there is a write up with a few pics http://www.ybw.com/forums/showthread.php?t=297335

 

[Dave_Seager]

Bear in mind that not all 270 legs were created equal. They have different gear ratios for different applications. Depending of which 270 version you have, they were originally available with three or four different gear ratios. Higher ratios were normally used for diesel engines to compensate for their lower engine revolutions. Although the wrong ratio can be compensated for by changing the propeller pitch it can lead to and very coarse pitched propeller if you use a leg intended for a petrol engine with a diesel.

You can see the various gear ratios at http://www.volvopenta.com/SiteCollectionDocuments/Penta/Misc/drive_2_oil_rec_7745608.pdf

 

[PaulGooch]

The Peugeot 2.0 diesel engine is a common rail engine, many of car installations of the 110 BHP versions used the particulate filter system, you'll want to avoid those ones. Early 406's will probably be the best choice, but finding one with sensible mileage will be almost impossible.

 

[Latestarter1]

In suspect that the OP actually refers to the 1.9 XUD Series as I assume that he is using the Bowman combined HX.Manifold, however you are correct in that they ended in the late 90's and finding two low mileage units is going to be a challenge.

Later common rail engines with after treatment not an option.

Do not wish to pour cold water on the project, however I think that the days of marinising old car engines is pretty much over. The Perkins Prima turbo from Montego would do the the job well, however they are now like hens teeth.