Bolt on Surface Drives/ Rudder.

[MapisM]

crazy idea. Buy a surface drive prop and try it on an outboard motor raised vertically on a small frame, to see if it works!

Not a crazy idea at all.
Some high power O/Bs are available with a specific lower case designed for surface propellers (one example is in the pic below).
Oh, and they also invented hydraulic transom mounts to fine tune the O/B height according to the speed (see youtube video below), something only allowed by O/Bs, of course.

PS: In your boots, I wouldn't even bother researching the topic further for a boat like yours, anyway. These things only make sense in the 50+ knots territory.

 

[rustybarge]

If only petrol was the same price as the in the States.....

Jack plates seem to be very well engineered solution to getting the prop at the perfect depth for max performance.
Those Yanks know a thing or two about outboards.

 

[Portofino]

Does this qualify as a " crazy idea"?
http://www.arneson-industries.com/page.php?type=products&id=bravoConversion

 

[rustybarge]

Does this qualify as a " crazy idea"?
http://www.arneson-industries.com/page.php?type=products&id=bravoConversion

Apparently Outdrives are so bad, that converting them to surface drive makes sense!

Looks like you don't need a special prop for surface drive....

The ASD6 Kit has a 26 tooth spline propeller shaft, same as the Mercury SSM#6 drive units, removing the need for any special propellers as the standard Mercury Speed Master propeller will fit the propeller shaft. Rolla and Hering also fit the propeller shaft.

NB: the Merc speedmaster is a surface drive prop for the outboard conversion.

 

[MapisM]

NB: the Merc speedmaster is a surface drive prop for the outboard conversion.

Conversion from what? Speedmaster props are just the cleaver propellers designed to fit the speedmaster shaft, nothing else.

That aside, outdrives are NOT "so bad" at all.
For small(ish) pleasure boats, and up to "normal" speeds like 30 or even 40 kts, they are (together with O/Bs) the most efficient transmission known to mankind, period.
Way better than surface transmissions in most respects, and if properly maintained, they are reliable enough for such applications.

Things like the ASD conversion kit are aimed at insane folks - of which in the US there's plenty - which put 800 or even more HPs through a Bravo outdrive designed (in its stronger version, the XR) for no more than 600. And when they blow the outdrive(s), some of them try the ASD kit route.
But just a very few, and with varying success, afaik. Those who want to go real fast, rather than spend their days and nights in the garage, simply bite the bullet and go for a proper setup with outdrives designed for surface props, like the #6, that can withstand 1000+ HPs.

Geez, this debate is beginning to resemble a car tuning discussion, with folks thinking that they know better than VW and can make their Golfs run better by tweaking this or that...

 

[rustybarge]

Conversion from what? Speedmaster props are just the cleaver propellers designed to fit the speedmaster shaft, nothing else.

That aside, outdrives are NOT "so bad" at all.
For small(ish) pleasure boats, and up to "normal" speeds like 30 or even 40 kts, they are (together with O/Bs) the most efficient transmission known to mankind, period.
Way better than surface transmissions in most respects, and if properly maintained, they are reliable enough for such applications.

Things like the ASD conversion kit are aimed at insane folks - of which in the US there's plenty - which put 800 or even more HPs through a Bravo outdrive designed (in its stronger version, the XR) for no more than 600. And when they blow the outdrive(s), some of them try the ASD kit route.
But just a very few, and with varying success, afaik. Those who want to go real fast, rather than spend their days and nights in the garage, simply bite the bullet and go for a proper setup with outdrives designed for surface props, like the #6, that can withstand 1000+ HPs.

Geez, this debate is beginning to resemble a car tuning discussion, with folks thinking that they know better than VW and can make their Golfs run better by tweaking this or that...

I dispute your conclusions!

Here's a Cat cruising at 25 kts with twin cummins C.450hp and Seafury surface drives...

"Six years ago 'Cougar Cat" on the Gold Coast, Queensland, constructed a 12 metre Power Catamaran to suit our requirements for operation in the Torres Strait.

In order to travel in the range from 22 to 25 knots, loaded, we specified Cummins C Series motors (450hp), Twin Disc Gearboxes and Seafury Surface Drives.

The SF26 Seafury Drives enabled the 12 tonne Robert Henry to get out of the hole and onto the plane easier and faster than any other drive system we have experienced on our previous vessels.

We now have 7000 hours on the machinery and only have had to change the SF26 drive bushes and seals every 2500 hours. They have provided smooth, economical operation with the added benefit of reduced engine noise as the exhausts vent underwater directly in front of the propellers.

We are planning to acquire another new vessel in the next 2 years and we will certainly be utilizing Seafury Surface Drives."

SANDIE AND GREG EDWARDS
Owner/Operator
Australia

View attachment 36858View attachment 36859

 

[Portofino]

Conversion from what? Speedmaster props are just the cleaver propellers designed to fit the speedmaster shaft, nothing else.

That aside, outdrives are NOT "so bad" at all.
For small(ish) pleasure boats, and up to "normal" speeds like 30 or even 40 kts, they are (together with O/Bs) the most efficient transmission known to mankind, period.
Way better than surface transmissions in most respects, and if properly maintained, they are reliable enough for such applications.

+1. I agree here mine 10 y old VP. DPG have been great ,reliable etc but as MapishM infers it's all down ,or seems to be linked to proper maintained .
There are a lot around both Merc+ VP in the sub 40 ish foot sports boat sector and they work well .

 

[rustybarge]

+1. I agree here mine 10 y old VP. DPG have been great ,reliable etc but as MapishM infers it's all down ,or seems to be linked to proper maintained .
There are a lot around both Merc+ VP in the sub 40 ish foot sports boat sector and they work well .

I think problems with outdrives occur when they are left in the water all year long, there are a lot of gaskets to go wrong. From a mechanical viewpoint putting the drive train through two 90 degree 'bends' is going to put a lot of stress on the gears and shafts, and all the rubber bellows etc on or under the waterline just waiting to leak.

An outdrive is a very complicated and expensive engineering solution when you compare it to the simplicity of a shaft running in a rubber cutlass bearing.

what roughly have you spent maintaining your outdrive over the 10 years period?

 

[MapisM]

I dispute your conclusions!
...

Feel free!
But if you're so concerned about otdrives reliability, stick to shafts, accept a lower efficiency, and call it a day.
Forget surface drives, whatever you can read on a builder website is bound to be a tad biased.
I've recently been in Cairns and Port Douglas, where there is the highest concentration of big catamarans for tours to the GBR, and guess how many had surface drives? Zilch. Btw, I've also been onboard a couple of them, and they were both faster than that Cougar Cat thing...
I'm not saying that Seafury is lying, just that surface drives are NOT the best choice, for anything else than extreme speeds, period.
Then again, if you're interested by weird applications of surface drives, have a look at this video.
Around 3:20 you will see surface props spinning, in spite of the fact that the monster is only capable of slow displacement speed.
But exceptions are, well, exceptions - and usually there are very specific reasons behind them.
Bottom line, I don't mind if you dispute my conclusions, the boat for which you're considering these transmissions is yours, after all.
But you also thought that with surface drives the shaft is above the w/l...

 

[rustybarge]

Weird or What.

Reminds me of Stargate the movie, when the alien arrives on the planet in a Pyramid shaped starship......

NB: I'm acting as a bit of an 'Agent provocateur' regarding surface drives. If they were that good, there must be some reason why they're not on every boat.

 

[MapisM]

If they were that good, there must be some reason why they're not on every boat.

Indeed.

Oh, and just for your further info, also "normal" outdrives can be installed higher than their standard position, which is with the cavitation plate aligned with the keel.
This way, you still get a decent maneuverability and hole shot, while reducing high speed drag.
My last lake boat had a Bravo outdrive, with a 4 blades (non-cleaver) prop, but the prop shaft was just 3" lower than the keel (hence the cavitation plate was 5" above its standard position). This meant that the 15" diameter prop worked submerged only for 2/3, at speed. And the nose cone was barely under the water surface, particularly with the outdrive trimmed out.
Such setup, that I understand can seem a compromise (ermm... and it is, tbh ), is actually very common with performance boats designed to be very fast, but not extremely fast.
I mean, my boat was good for 70mph with the stock 496 engine, but I've been on another identical one capable of 85mph, courtesy of a tuned 496 with 600hp.
And also the latter had the very same Bravo outdrive installation.
Though that's actually borderline. Above 80mph, it's normally pure surface props territory...

 

[rustybarge]

Indeed.

Oh, and just for your further info, also "normal" outdrives can be installed higher than their standard position, which is with the cavitation plate aligned with the keel.
This way, you still get a decent maneuverability and hole shot, while reducing high speed drag.
My last lake boat had a Bravo outdrive, with a 4 blades (non-cleaver) prop, but the prop shaft was just 3" lower than the keel (hence the cavitation plate was 5" above its standard position). This meant that the 15" diameter prop worked submerged only for 2/3, at speed. And the nose cone was barely under the water surface, particularly with the outdrive trimmed out.
Such setup, that I understand can seem a compromise (ermm... and it is, tbh ), is actually very common with performance boats designed to be very fast, but not extremely fast.
I mean, my boat was good for 70mph with the stock 496 engine, but I've been on another identical one capable of 85mph, courtesy of a tuned 496 with 600hp.
And also the latter had the very same Bravo outdrive installation.
Though that's actually borderline. Above 80mph, it's normally pure surface props territory...

Thanks for that info.....raising the outdrive, Now that's something I never considered.

 

[Portofino]

what roughly have you spent maintaining your outdrive over the 10 years period?[/QUOTE]

I don,t think £££ spent comes in to it really .Reason any perceived extra cost over A N other propulsion system is recouped at the fuel pontoon .
It's a conscious leisure decision for me boating ,like purchasing the mooring buying flights or holiday property .
I drive a Ferrari but realise other cars cost less to buy and service and have a better MPG cheaper tyres etc .
Nobody held a knife to my throat when I bought the boat or the car .Both have been 100% reliable .
i like outdrives they work for me cos at the mo I like the extra zest and sporty performance higher cruising speed and ecomonical 28-30 knts @ 60-70 L. / hr at 3000 rpm ( wot 3700ish ) .
I,am not knocking flybridge shaft boats or any others it's individual choise each to there own .

I don,t understand this race to the bottom with boat maintaince ? Or motoring costs .or other none essential leisure activities .

 

[rustybarge]

what roughly have you spent maintaining your outdrive over the 10 years period?

I don,t think £££ spent comes in to it really .Reason any perceived extra cost over A N other propulsion system is recouped at the fuel pontoon .
It's a conscious leisure decision for me boating ,like purchasing the mooring buying flights or holiday property .
I drive a Ferrari but realise other cars cost less to buy and service and have a better MPG cheaper tyres etc .
Nobody held a knife to my throat when I bought the boat or the car .Both have been 100% reliable .
i like outdrives they work for me cos at the mo I like the extra zest and sporty performance higher cruising speed and ecomonical 28-30 knts @ 60-70 L. / hr at 3000 rpm ( wot 3700ish ) .
I,am not knocking flybridge shaft boats or any others it's individual choise each to there own .

I don,t understand this race to the bottom with boat maintaince ? Or motoring costs .or other none essential leisure activities .

The race to the bottom are costs:

50' planing boat £750k, depc. £150k
mooring Sof F ............. £50k
lift out antifoul, outdrives etc...£5k
Extended summer cruise around Corsica, Sardinia, Sicily and back(10 weeks)..£70k ( super conservative)
Extra slush fund £10k (insurance flights etc)

total / year for tiddly little 50' boat: £285k.

I'm making the persumtion you are going to cruise in your boat, not sit in a floating caravan.
Capital needed to fund expenditure after tax: about £15m.

 

[abraxus]

I think problems with outdrives occur when they are left in the water all year long, there are a lot of gaskets to go wrong. From a mechanical viewpoint putting the drive train through two 90 degree 'bends' is going to put a lot of stress on the gears and shafts, and all the rubber bellows etc on or under the waterline just waiting to leak.

An outdrive is a very complicated and expensive engineering solution when you compare it to the simplicity of a shaft running in a rubber cutlass bearing.

what roughly have you spent maintaining your outdrive over the 10 years period?

Not sure what you'd consider reliable or expensive to maintain, but I have a an alpha one outdrive on my sportscruiser. I'm river based and the boat stays in the water all year. The drive is serviced every two years at a cost of about £300, and is now nearly 25 years old and has been trouble free in the 14 or so years I've owned the boat.

 

[rustybarge]

Not sure what you'd consider reliable or expensive to maintain, but I have a an alpha one outdrive on my sportscruiser. I'm river based and the boat stays in the water all year. The drive is serviced every two years at a cost of about £300, and is now nearly 25 years old and has been trouble free in the 14 or so years I've owned the boat.

That's a solid record of reliability.
Google nearly any product, and you will get a raft of problems that may not affect the majority of owners. It s extremely hard to find out how good a specific design really is.
.....but there are plenty of bad ones, as well as the good ones.

 

[MapisM]

Google nearly any product, and you will get a raft of problems that may not affect the majority of owners.

Without even trying, I bet this is true also for the Merc Alpha.
Otoh, it's by far the most popular outdrive for boats up to 25' or so, and there are zillions of them around the globe.
Pretty sure you'll find less problems reported for the Seafury or the ASD kit for Bravo, if you see what I mean...