Sterndrive or Inboard ?

[Romeo]

Righto, I am looking at buying a motor boat for the first time, after many years of sailing (sans engine btw). Must be a mid life crisis of some sort, maybe I will recover.

I am hoping to get a displacement cabin cruiser of about 30 feet. My perhaps non standard requirement is that I need it to be able to take the ground from time to time in sheltered spots at low tide.

Of the two boats I am looking at, one has a diesel engine close to the stern, with a stern drive. The other has a standard inboard with a propeller protected by the keel with the rudder behind it. Either of them would be able to take the ground, but I was wondering if the collective expertise on this forum could give a view with regard to the merits of sterndrive v standard inboard in a displacement cruiser. What effect on handling, manoeuvring, maintenance, etc etc.

Thanks in advance for your thoughts, R.

 

[BruceK]

You're going to start a war and become very unpopular with a question like that. Out of interest what displacement cruiser are you looking at that has a sterndrive / IO? It would be an odd combo for a displacement boat in my limited experience.

 

[MapisM]

merits of sterndrive v standard inboard in a displacement cruiser

If by displacement cruiser you really mean a displacement boat (which at 30 feet implies 8kts max, when you are in a rush!), that's a no brainer, imho.
Show me a commercial boat of that size which has anything else than a keel enclosed straight shaft, and I will eat my hat with vinegar dressing!

 

[[164147]]

You're mixing engine types (Inboard / Outboard) and drive types (Sterndrive / Shaftdrive etc).

You might find a semi-displacement hull with a sterndrive but not a displacement hull that I'm aware of?

The pensioners on here love their shafts - but then if we'd all be living in caves if it weren't for the adventurous I have no problem with either - just depends on the type of boat and boating you like.

 

[BruceK]

The pensioners on here love their shafts - but then if we'd all be living in caves if it weren't for the adventurous

Sheer bloody brilliance. Now any nay sayer of legs implicate themselves as not only being Luddites but also troglodyte old fogeys. Nothing like getting the dagger in first

 

[MapisM]

You're mixing engine types (Inboard / Outboard) and drive types (Sterndrive / Shaftdrive etc).

Yeah, but even us pensioners living in caves understood what he meant regardless...

 

[KevB]

I love my boat with sterndrives and unless going bigger than 40' would stick with them but..... in your case with displacement I would choose shaftdrive but..... sterndrives would generally give you more usable cabin space.

 

[Murv]

Speaking as somebody well over 20 years from pensionable age... I'd probably choose shafts. Or an outboard. Or oars. Or a team of trained hamsters in wetsuits. Or just drifting off into the tide and hoping for the best. Just about any means of propulsion that doesn't involve an outdrive really.

Just personal opinion though

 

[Romeo]

You're going to start a war and become very unpopular with a question like that. Out of interest what displacement cruiser are you looking at that has a sterndrive / IO? It would be an odd combo for a displacement boat in my limited experience.

The one I am looking at is one off right enough. Sounds like that is not a surprise from the comments. But why is that? What is the downside that makes it so rare? In other aspects it is a boat that ticks a lot of boxes, the engine free accommodation being one of them.

 

[BruceK]

Throw me to the mob then. I think the diplomatic answer is in a displacement boat none of the benefits of an IO are realised and all its failings thus amplified. Tbh I'd rather go displacement with a small outboard than IO if internal cabin space was the goal.

 

[superheat6k]

Not a difficult one this at all - shaft of course !

 

[simonfraser]

'My perhaps non standard requirement is that I need it to be able to take the ground from time to time in sheltered spots at low tide'

you'll need a stern drive then, that lifts up out of the way, and the bottom will be relatively flat / boat relatively horizontal

 

[Firefly625]

The pensioners on here love their shafts - but then if we'd all be living in caves if it weren't for the adventurous I have no problem with either - just depends on the type of boat and boating you like.

I'm not a pensioner, & sub 50, still shafts ALL the way.

Although a close second would be hamster power.

 

[Firefly625]

'My perhaps non standard requirement is that I need it to be able to take the ground from time to time in sheltered spots at low tide'

you'll need a stern drive then, that lifts up out of the way, and the bottom will be relatively flat / boat relatively horizontal

I have beaching legs for that.

 

[Romeo]

I'm not a pensioner, & sub 50, still shafts ALL the way.

Not a difficult one this at all - shaft of course !

If by displacement cruiser you really mean a displacement boat (which at 30 feet implies 8kts max, when you are in a rush!), that's a no brainer, imho.
Show me a commercial boat of that size which has anything else than a keel enclosed straight shaft, and I will eat my hat with vinegar dressing!

Throw me to the mob then. I think the diplomatic answer is in a displacement boat none of the benefits of an IO are realised and all its failings thus amplified. Tbh I'd rather go displacement with a small outboard than IO if internal cabin space was the goal.

Hi folks, you are forgetting that the Q is coming from someone who is new to this whole mobo thang. I am looking at second hand boats, one of which has a sterndrive, and one of which has a shaft drive, both of which will probably give me 8 knots max, which is fine by me (and twice the speed I go at just now)!

It would be great if someone could expand on the reasons why a shaft drive would be better, rather than just implying its bleedin' obvious. If it was bleedin' obvious to the newbie, I would not have asked the question! Your patience is much appreciated, R.

 

[BruceK]

It's been done to death. Have a search. Not trying to be difficult. I am not sure anyone really knows for sure but they sure are partisan to their preferences. It's almost religious.

http://www.ybw.com/forums/showthread.php?454723-Legs-vs-shaft&highlight=legs+vs+shafts

http://www.ybw.com/forums/showthread.php?451919-Ips-v-legs-v-shafts&highlight=legs+vs+shafts

http://www.ybw.com/forums/showthrea...ms-with-shaft-drives&highlight=legs+vs+shafts

http://www.ybw.com/forums/showthrea...-boat-with-Outdrives&highlight=legs+vs+shafts

 

[Murv]

The two main advantages of outdrives are:

1) Better fuel efficiency at speed

2) The ability to lift the prop at the touch of a button to clear any fouling


1) Would not apply to a displacement boat

2) Would not be a good enough reason for me given the potential source of unreliability from an outdrive (personally)

Another thing that may be worth considering... if you're drying on hard ground and reliant on lifting the outdrive, what would you do when the lift mechanism fails?

 

[billg]

Hi folks, you are forgetting that the Q is coming from someone who is new to this whole mobo thang. I am looking at second hand boats, one of which has a sterndrive, and one of which has a shaft drive, both of which will probably give me 8 knots max, which is fine by me (and twice the speed I go at just now)!

It would be great if someone could expand on the reasons why a shaft drive would be better, rather than just implying its bleedin' obvious. If it was bleedin' obvious to the newbie, I would not have asked the question! Your patience is much appreciated, R.

An outdrive is an odd choice for a displacementboat, because their real payoff comes with the ability to trim the drive angle of the leg. However, I can see some possible utility in them for displacement use, so here is my list of pos and neg points

NEGATIVE
1) Maintenance costs are way higher than shafts. The outdrive is a complicated bit of kit which has to turn many HP through 90 degrees twice. Its watertight integrity is determined by one or more rubber belows which prudence dictates should be replaced well before any possibility of failure. More of the routine maintenance items are below the waterline and can only be accessed during liftout.

2) The boat steers by turning the outdrive and so max steering angle is usually quite small -- this doesn't matter at 30kts but certainly does at 8. The pseudo rudder provided by the leg is quite small so steering while moving with the power off, while not absent , is further restricted. These factors combine to imply that most boats with OJ's qre quite "wandery" at displacement speed -- that is they require constant attention to maintain a respectable course and larger steering inputs than you would expect to restore direction once lost.

POSITIVE
1) You have vectored thrust at the stern which means that steering at berthing speeds is much better than a single engined shaft boat (which usually uses prop-walk to achieve the same effect -- less well and only in one direction). Indeed if you have a bow thruster a bit of practice will allow you to move a single engined OJ equipped boat more or less directly sideways with minimal fore and aft movement

2) The ability to trim the leg means that you can get access to a fouled prop without swimming.

3) The geometry of the installation means that the engine is under the stern-deck and is thus easy to insulate accousticaly from the wheelhouse/accommodation, whereas a shaft boat typically has the engine underneath a centre wheelhouse -- which pretty much guarantees high noise levels. To give you an example, our boat, which has a 350Hp diesel on an outdrive and an enclosed centere wheelhouse is quieter inside at 30kts than my car is on the motorway. This may matter less on a displacement boat with a 50HP engine, but a recent trip on a friend's displacement boat with a single engine on a shaft showed just how tiring and irritating the noise level on such an installation can be -- and at 8kts it goes on for a good while too.

Hope this helps

BILL

 

[Nick_H]

I think the main advantages of outdrives (in comparison to shafts) are:

1. they allow the engines to be pushed aft, so freeing up space for bigger cabins
2. they are much cheaper for boat builders to fit
3. They have better fuel efficiency at higher speeds
4. They make smaller boats more fun to drive at higher speeds
5. they can be raised to free fouling or clean the props, or allow beaching

The disadvantages are higher routine maintenance costs (although partially offset by having smaller engines), and much higher risk of failure requiring expensive repair and/or affecting holiday plans. Outdrive boats also tend to wander more at low speeds.

For me reliability is first, second and third priority so I wouldn't have outdrives, despite all of their advantages.

 

[Romeo]

Thanks Murv, Nick and Bill. All very helpful.