What propulsion system should I get?

[Shaftbomb]

Next year we should be getting a 25ft locally built boat.  My boat builder said that regarding engines, I have all options open.  If i want I get invest in two big outboards, two inboard marine diesels with traditional shafts or with jolly surface drives or zdrive.  The boat is the fast fisher type and has a beam of over 9ft...what do you think is the best system I should put my eyes on?  Pros and cons, fishing capability and speed?? 

[skip]

Surface drives are seriously expensive and don't think needed for your type of application.

Personally after using a Z-drive boat for 15 years I would say don't bother with them if you're planning more than 70 hours per season as the wear and tear and associated maintenance costs becomes too high.

Up to 100 hours, outboards are a good option and over 100 hours per year then move to shafts.

I'm a fan of modern outboards but I think on that boat, twin inboards on shafts are probably the way to go, especially for fishing and to keep lots of space on the transom area.

[shanook]

If the boat is for fishing then its a definite shaft system. If its speed u need then its outboards...Personally I dont like z drives too much trouble...

[skip]

To second Shanook, outboards will force you to retreive your fish from the side of the boat as twin's will take up space. On a 26 foot I would imagine you're looking at twin 120 or twin 150's so like Lm4500 per engine!!

For those prices I'm sure you can get some converted marinised engines on shafts most probably for less.

[Shaftbomb]

I know that modern outboards offer speed, quietness and smoothness in the ride but having the transom occupied with them is not something I like....even when fishing, I would have to fish from the sides, a big down when fishing for lampuki.
We would use the boat for fishing and pleasure, not more than 100 - 120 hrs a year (may be even less).  My boat builder advised that with a twin yanmars with shafts we would have over a 40-45mph speed but then the boat is limited to that speed, while with surface drives we could have a top speed in the 60s.  I know they are very expensive but may be I can find two good price ones from the internet.  My concern is if they give trouble like zdrives or if they have a lot of maintenance because I had a regular shaft boat for 10 years and was maintenance free regarding propulsion system....

[skip]

With boats you need to very much choose what you want it for and then base everything around that. To me surface drives only serve two main purposes: Speed/Performance, lower draught in the water in case you need to go in shallow places alot.

But bear in mind with surface drives that you have your drivetrain sticking out at the surface, I would say totally un-tuna/albacore friendly, you'd freak them out when you were retreiving them and they were near the boat!

Whilst I'm sure the boat may well do 60mph, 52knots or so, the boat I used to use would do 40 knots flat out and she was 32 feet, once you start going above 30-32 knots in a 26 foot+ boat everyone is hanging on for dear life and the boat is taking quite a pounding, let alone over 45 knots where you would need very idea conditions.

To put surface drives on that boat you're basically building a 'racing fishing boat', is that really what you want to do?? I also don't think surface drives are hassle free compared to shafts, you're back in similar waters as Z-drives maybe.

Personally I would say, go with good shaft, match up your props and gearbox ratio to give you the top speed you want, but also are you factoring in your consumption?? Modern large turbo aftercooled diesels like Yanmars are heavy, and I reckon you'll be happily burning 50-60 litres per hour at a decent cruise speed. With diesel being priced more than petrol, you'll want to be towing a fuel station behind you!!

To me I would be more interested in a set up that let's the boat stay on the plane at relatively low speeds like 13-15 knots and maybe give you a cruise of 25-28 knots which I reckon is a very good compromise. Let's be honest, how often do people run at close to full throttle all the time, except for Shanook!!!

The choice of course is yours.

[Shaftbomb]

Regarding fuel consumption I know its a problem but hej whatever you buy eats fuel.....the last boat I had was powered by an Iveco 130hp turbo diesel.  When I compare the diesel it consumed twelve years ago and the diesel it consumed one year ago, I can say that it quadripled!  Outbaords eat fuel too.  From what i read on the net, I think the most fuel efficient diesel unit available right now is the Steyr engine.  But i dont know about the reliability and longitivity of the engine. 
What I would love to have is a racing fishing boat...but I do not know if that is achievable.  Although im really tempted to buy surface drives I want to know more what are the issues with them and what maintenance do they require.  In Malta and Gozo it's quite hard to find opinions on them because I do not know of any boats equiped with such a power unit....

[The_Gaffer]

Hi Shaftbomb, My trojan is repowered with a Steyr Hi Power 246 marine turbo diesel engine.  The fuel consuption is very low, and reliability is high.  My boat weighs in at over 5 tons, and with one engine I can cruise at 20knts and top speed is 25knts. 

[Shaftbomb]

Hi Gaffer...you just have one engine in that boat?  I saw your boat in the gallery section and I think I saw it a couple of times at comino too.....looks fast!

[bigboy]

Shaftbomb id go for inboard engines. Why dont jou consider having a big engine in the middle saying maybe a 6 cylinder engine with turbo and then having a 4 cylinder on the side. It would be quite good as you can troll and fish using the small engine.

[Shaftbomb]

The boat my father sold last year had a setup like that, an iveco in the middle and a yanmar 18hp  next to it.  For fishing it was great but had many many disadvantages.  First of all, when you see the boat on the pontoon, it is always tilting on the yanmar side.  When reversing to get in the pontoon it was always a hassle because the boat never obeyed!  Another disadvantage was when turning to the right (the small yanmar was on the left side of the boat) we had always to take wide turns because the boat never obeyed even though it had twin rudder.  Top speed also was much lower than those who had a single iveco engine.

[skip]

http://www.powerandmotoryacht.com/features/0604surfacedrives/

Take note the article says that boats should be built specifically for surface drives from the initial design phase! Questions I would be asking are have Petecraft ever installed surface drives on their other boats. How did they perform, have you gone out for a test run in them etc! I wouldn't let myself be the guinea pig, if it's something they want to offer customers, they should build themselves a demo boat with surface drives so that they can adjust the design accordingly if needed.

http://www.nauticexpo.com/boat-manufacturer/surface-drive-1983.html

[Shaftbomb]

I don't think there is a boat with surface drives in Malta.  I know that petecraft did make one like 5 years ago but the surface drive he used was fixed, that is, it did not move.  The surface drive was attached to a yanmar 350hp and installed on a 22 ft boot.  The boat had a top speed of 50mph, but the owner was not happy with it and swithed to a verado outboard this year...