Small boats - sterndrive versus shaft?

[MotaBota]

Thanks for all the advice on my other post about merry fisher type boats.

Can anyone tell me why pretty much all the sub 8m boats of this type have shafts when a sterndrive would use less fuel and go faster?

Most of the 7m MF's have around 150hp of diesel power but struggle to crack 20knots and do so noisily. The outboard versions with the same power go much faster with the same power, presumably due to not having the drag of a shaft etc.

There must be a reason why they have shafts - cost? Something to do with fishing?

Anyway - I'd like a MF type under 8m with a diesel sterndrive. So far I've only found the Quicksilver 640 which i think has it - can the illustrious members of this forum point a noob towards any others or enlighten me as to why they don't make then and why I'm being daft?

Many thanks! /forums/images/graemlins/grin.gif

 

[Bandit]

My experience is of the Ocqueteau range which is well worth considering and a very similar range model for model as the Jeanneau and Beneteau ranges of the peche promenade style, all do outboard and inboard diesel.

There are several factors to consider:

Stern drive gives about 25% more thrust and is very effficient.

There are big advantages of diesel over petrol from a running cost.

A stern drive costs about as much to service again as an engine.

Diesels cost more to buy than petrols.

Shaft drives if well maintained cost little to maintaine except a cutlass bearing change every few years say 5 on average ?

Stern drive has the engines just inside the transom from a trim point of view.

Outboards are as efficient as stern drives but almost always petrol.

With outboards the weight is outside the transom.

Diesels generally last longer than petrols.

Boats like this have a small keel holding the prop shaft which gives some protection to the prop from debris, it protects it from the bottom when drying out, as well some stability,

Diesels shaft boats feel much better in a seway as there is more weight of engine and fuel further forward splitting the waves, this is an important factor and makes the feel of similar sized outboard and shaft diesel boats feel very different.

The faster you go in moderate sea the more and harder you will slam.

Each of the above are trade offs against each other and personnal prefernece does come into it as well as cruising ground and budget.

If I was going for a 7+ metre boat of this type for use at sea I would go for diesel on shaft every time, condider the Ocqueteau 715 secondhand or the 735 new an excellent boat.

 

[omega2]

Shafts, almost bomb proof, and if any engine gearbox issues arise they can be fixed without a haul out. I had an outdrive she became known as yo-yo, no question for me Shafts every time.

 

[MotaBota]

Thanks for that - I'll have a look at the Oqueteau (and hopefully learn to spell it!).

From what you say, having the engine further forward is an advantage in a small boat, especially with Solent chop. I didn't realise sterndrive meant the engine was further back - I'd assumed a diesel engine would be mounted in the same place for shaft or sterndive. I assume therefore that the engine and sterndrive have to be bolted together, not the engine forward with a shaft linking it to the sterndrive.

Right, I'll have to have another rethink about what I need! /forums/images/graemlins/grin.gif

 

[Bandit]

In a stern drive the engine inside the boat, connects straight through the transom to the drive leg so the back of the engine is a foot or so ahead of the transom.

Generally on shaft drive boats such as these the propeller shaft line continues up into the boat and the engine is normally about amidships.

 

[AHoy2]

[ QUOTE ]

Most of the 7m MF's have around 150hp of diesel power but struggle to crack 20knots and do so noisily. The outboard versions with the same power go much faster with the same power, presumably due to not having the drag of a shaft etc.


[/ QUOTE ]

You need to take into account that (generally) the diesel inboard boats have semi-displacement hulls v. the planing hulls of the outboard versions.

 

[goochie]

Yep. If you can get a shaft boat with the Nanni 150 or 200hp engine based on the Toyota block, they are nigh on bulletproof.

 

[MotaBota]

[ QUOTE ]
[ QUOTE ]

Most of the 7m MF's have around 150hp of diesel power but struggle to crack 20knots and do so noisily. The outboard versions with the same power go much faster with the same power, presumably due to not having the drag of a shaft etc.


[/ QUOTE ]

You need to take into account that (generally) the diesel inboard boats have semi-displacement hulls v. the planing hulls of the outboard versions.

[/ QUOTE ]

Dammit! Don't complicate this any further! /forums/images/graemlins/grin.gif

I'm just getting my head round propellors and engines - I don't think i can cope with hull shapes just now! /forums/images/graemlins/confused.gif

This boating lark - it's a damn sight harder than picking a car! Think I'll just have a look round and buy what everyone else has! /forums/images/graemlins/wink.gif They can't all be wrong!

 

[whisper]

"shaftdrive..........engine about amidships" - is why they are so noisy in the wheelhouse.

Have a look at Phaeton and Ryds 23 - both have sterndrives. We've had a Ryds 23 - was excellent but we decided that open backed wheelhouse got a bit draughty in Winter. /forums/images/graemlins/blush.gif

 

[Bandit]

I agree the beauty of a boat like this is the closed wheel house with patio doors.

Try and ensure that the engine is completely outside the wheelhouse for noise and heat reasons and not half in and half out.

The Ocqueteau 715/735 is completely outside the wheel house.