Replacing Mercruiser 4.3MPI by a Diesel engine

[BartW]

I am new to this forum,
I am planning to replace the Mercruiser engine in my 24ft cruiser by a Diesel engine f.e. Yanmer 6BY260Z. This Yanmar engine is quite new, so I can not find very much info on the web about it. Does anybody know what kind of improvement I can get, does anybody have experience with Yanmar quality and service ?
my boat is a Faeton 730 sport, length 7.3m, weight 2000Kg
with mercruiser 4.3MPI, Alpha1 leg,
max speed is about 35KN
accelaration and planing is OK
This boat type is available from the factory with Volvo 160HP Diesel engine buyld in it,
Is it wise to put in a 6BY260Z Yanmar, or eventually the new Volvo D4, 300HP ? Or is it not possible to get some advantage from this over powering ?
What kind of leg should i Use,
Is the diffrence between single versus duoprop BravoIII drive noticable ?

 

[volvopaul]

The alpha 1 leg is only suitable for a petrol im told, a diesel has too much torque and will chew it to bits, you need the full yanmar package or consider a volvo d3 190 or d4 260/300 dont overpower though its pointless in spending more than you have to.

Im looking for a secondhand engine for a searay that im doing at the moment, is the petrol still a runner or not if so let me know please, maybe worth a look.

Do your homework and get quotes from other companies to compare as re engining doe not always up the value of a boat.

 

[Elessar]

I've done this sort of thing twice.

The first time was from a V8 merc to merc deisel.

The second time was to yanmar.

Issues.

Yanmar parts are expensive, so if you haven't got everything with your engine the project will sink you financially. eg exhaust 1200 quid, doughnut 1200 quid etc etc.

The yanmar will be too long for your engine bay in all probability as it's a straight 6. This was the case in my first conversion and it was flippin hard work to make it bigger.

Alphas I don't think will fit and they will certainly break very quickly. You'll need a bravo 1 x or bravo 3 x drive. The non x's will fail. The x's will fail if you don't fit a shower and draw cooling water through the leg as well as through a skin fitting. The water flow though the leg alone is not enough for a diesel and mercruiser sell a kit to blank the inlet, don't use the kit use a Y piece. The twin props do add a lot especially in a single installation, no prop walk, better low speed tracking etc.

You'll also need a bravo transom shield - the bravos all have the same shield but it's different to the alpha. You need to take some more off the transom not glue some on so that's OK.

You'll need to be good at wiring too to make the boat loom integrate with the engine, upgrade the battery wiring as well.

On my 31ft boat going from a big block V8 to a yanmar raised the waterline by about 2" - it was nearer 4" going from the small block V8 to the 6cyl merc on my 27 ft boat. Will your small boat still be stable (indeed will it float!)?

So in summary, take a look at another boat with the same instalation and make sure you've all the bits before you start.
And if you're not extremely industrious don't try it at all.

 

[Nautorius]

Bart,

In all seriousness I would sell the boat 'as is' and buy a diesel. You will spend more than it would cost to sell and buy again and it may never be right! I would only repower an older (over 10 year old) boat.

Cheers

Paul /forums/images/graemlins/smile.gif

 

[Sneds]

Have to agree with Paul.
We considered re-engining our 1988 Sealine 215 with a diesel, the cost was horrendous!
Spent the money on a newer diesel boat.
Good luck

 

[BartW]

I am aware of the differences between Alpha and Bravo X, so I was considering the Bravo III X package anyway,
I am not aware of these cooling systems for the leg, where can I get info ?
The interesting thing about this new type from yanmar is the weight, (400Kg inclus Leg) and the size, similar to the Merc V6. (This Yanmar is a V6 by the way)
I am not planning to replace this boat, as it is the perfect solution for my usage
- for diving; easy acces to the swim platform and a big open afterdeck,
- some basic features for Overnight weekender and cruising
- extremely good behaviour, B-category, 8 people
- and last but not least trailarable, I am using the boat in the Med aswell as in the northsea
the only minor point is the difficult planing when the boat is fully loaded with 6 people and their diving equipment
thats the reason why I want to stay with exactly this type of boat.
The Merc V6+Alpha1 is for sale, it is in perfect condition, 2005, 300Hr.

 

[gingie]

The new Yanmar is a straight 6 and this new application does not run a shower on the drive unless in hi-speed installtions i.e a Rib where we now fit a shower drive. which fits to the drive and has pipes that are force fed water as the boat moves and the pipes spray directly over the top end.
Depends on engine bay but the new 6 pot yanmar is the same size as the 4LH 240 hp 4 cylinder Yanmar. Its only available with X-drive.
Many issues with them at the moment which are slowly getting ironed out. Big lack off dealer training as well at the moment.
The D4-300 is a big heavy engine and i guess if the factory recommend it its ok if they dont there is a reason for it. Boat design, water line lengths with exhaust due to weight etc etc.

 

[vanoord]

I'd be surprised if the 6BY would fit into the boat tbh - it won't fit into a Monterey 275, which is somewhat larger: similarly, I'd ask some questions about the weight of a 6-cyl diesel in the back of a boat that size.

 

[MapisM]

[ QUOTE ]
max speed is about 35KN
accelaration and planing is OK

[/ QUOTE ]
And you're thinking to repower...
You already knew you shouldn't even think about that, didn't you?

 

[BartW]

It becomes more and more obvious that I should stay with the Merc 4.3MPI Alpha, but the Yanmar seemed such a good replacement:
- Yanmar with leg is 408 Kg, Merc with leg is 393Kg
- Yanmar size is same as Merc, see specs
- Yanmar is modern technology Diesel, Canbus, ...
- Better driving with duoprop (?)
- improved planing when fully loaded
My Alpha One leg suffers a lot when I am fully loaded with divers or kids, I am afraid it will let me down one day. When I replaced the oil from the Alpha leg (<100Hrs) this was almost black
So the yanmar /Bravo3 seemed a good, modern solution.
Now I am afraid,
until today i can't find any real live positive experience with this engine, apparently it is still in a prototype testing phase
Also Yanmar is very quite with info,
does anybody know an experienced 6BY260Z Yanmar dealer,
On all other "Diesel" alternatives I have looked at, the power to weight and size ratio is not as good as on this Yanmar
http://www.yanmarmarine.com/products/pdf/BY/6BY260Z.pdf