advantages of a surface drive?

[thudpucker]

Has anybody ever showed a demonstratable advantage of a surface drive over an I/O?
It seems to me your working with only one Oar with just the bottom half in the water!

[whitepointer23]

do a search pucker, there was a really good discussion on this topic a few weeks ago.

[CDK]

The advantage is mainly in the construction. Compare the number of submerged parts between an I/O and a surface drive. What isn't there cannot break down.
Also there are less friction losses: two angled gearboxes is not the most effective way to convey power.

The analogy with one oar is nice though, but when you watch a surface drive at work, you'll see that the top half does more than just hit air. The whole prop throws out a mixture of water and air. The noise and vibration are a disadvantage vs I/O.

[thudpucker]

Many thanks CDK.
I was wondering what the Reason for the Invention was. Simplicity is probably the answer to that question.

This site is good because of all the Time Zones of contributors. It's a 24 hour site with a lot of good information.
Dick

[Frosty]

Originally Posted by whitepointer23

do a search pucker, there was a really good discussion on this topic a few weeks ago.

Absolutely--this subject has been hammered to death and only one person is allowed to talk officially on surface drives. Any one daring to suggest an idea or notion will be attacked with fanatical rhetoric for offering an opinion.

On your head be it.

[IMP-ish]

Durability is a big plus. Look at the number of people who switch from bravos to surface drives. After they bite the bullet and spend the green, how many ever switch back to stern drives.

Reduced drag is a big plus. Getting the prop further back and up means less drive dragging through the water. Performance guys with stern drives spend 5-10k for shorties. This raises the prop by 1, 1.5, or 2" and can get a mph or two on the top end. They also make extension boxes to move the prop further back in conjunction with up. Also look for comparisons with outboards on transom brackets and jackplates.

I'm still trying to talk the family into a Formula 311 with kaama surface drives.

Comparing to the same hull with TRS drives and the same basic engines, owners with the kaama drives report a 5-10 mph gain in top end over the TRS owners.

[rasorinc]

http://www.well.com/user/pk/SPAprofboat.html This article explains it well.

[gonzo]

Surface drives use ventilated propellers. That allows them to have much higher blade pressure without cavitating. As a result they can turn a smaller propeller at higher RPMs. The gains are at the top end.

[thudpucker]

Hmmm, maybe for Shallow water use. Weeds can wrap a Jet drive up but are not as difficult with a hi-speed prop.
So a Hi speed prop, half in the water might go up a river in the long grass with less of a problem. Excluding rocks of course.
But a Skeg on the drive housing might keep the Rocks outta the prop as well.

Really I was just wondering if it had ever been demonstrated in a fair test that a surface drive was more useful or better in some way than an I/O?
I'll read that long NA's treatis later. Too early for heavy tech this AM.

[tom kane]

If you build your drive so that you can use it in both modes you can have a choice of which you prefer, and soon see the disadvantages of just surface drive mode.

[gonzo]

Yes it has. That is why in some racing types surface drives win.

[tom kane]

To get good steering with a surface drive you would need to have a deep rudder set about where it would be if it were conventional drive,so shallow draught is not available with surface drive.
There would not be many race boats that do not run surface drive.

[IMP-ish]

To get good steering with a surface drive you would need to have a deep rudder set about where it would be if it were conventional drive

I think that the skeg with surface drives is several inches above where it would be for either inboards or stern drives.

[tom kane]

If you use a rudder with surface drive or even a conventional drive the rudder needs to be in dense water to give more positive stearing. you can if you wish mount a rudder that slides up in it`s mounting when hitting the bottom. Rudders are not a good way to manouver a boat,stearable and trimmable drives are more pleasurable to use.
Any hull that is deep v is not realy a shallow water navigating contender. the deep draught plus the rudder and skeg plus the hole in digs in the water to get on plane rule that out. I would call 4 to 8 inches shallow water.
I could not imagine a recreational boatie setting his rudder of set and perhaps even the drive shaft to get better performance and handling, it would not look good.

[ChrisN67]

I have had personal experience with surface drives. I purchased an intrepid and had a refit from twin outboard to Yanmar Diesels, 2 speed transmissions and SBM surface drives. All in all the design of a surface drive is more resilient, and remarkably more efficient over 30knts (parasitic drag is a cube of speed).

I personally rebuilt the drives from the ground up and they are very simple to understand and install. My personal installation employed Aquadrive CV joints which will reduce vibration to a minimum.

Much of the conversations on this site sometimes drift into "masturbatory" conversations designed to assert dominance and prove expertise rather than have candid jovial discussions among people who share the same interests.

I would like to avoid this; and so I only offer the personal observation that surface drives do not have the same ability to hold a speed as do stern drives. I think this is due the propeller ventilation increases when loaded (resistance) is applied. So if you are operating in heavier sea-states, the surface drive would have a more difficult time maintaining consistent speed as opposed to a fully submerges drive system.

It is also a little more challenging to maneuver in tight quarters.

I am not an expert, so my observations are only that. If someone was truly interested in purchasing a production, reliable, surface drive drive system I recommend calling Rick at Arneson Industries.

I hope to have my boat in the water by the end of this month.

http://constellationq8.com/work