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Jul 03, 2014, 09:06 AM
Registered User
Discussion

How to set up for surface drive?


Probably a noob question that's been answered a lot but i cant seem to find anything on it. How do you set up for a surface drive? I know the prop shaft should come out of the transom but where abouts on the transom? Does the prop shaft need to be flat and if tilted at an angle what effect would that have? How far out should the prop shaft extend? I read somewhere that 10% or 5% of the boat length was the right amount but i cant remember which or where i read it.

Thanks in advance
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Jul 03, 2014, 10:01 AM
AndyKunz's Avatar
On a mono hull, right at the bottom of the V. The angle depends on the hull, prop, and power you're using. Generally you need a slight down angle to keep it from blowing off too easily. How far back also varies with power, prop, and hull.

I suggest you try one of the racing forums. My favorite is www.offshoreelectrics.com

Andy
Jul 04, 2014, 03:14 AM
Registered User
Thanks, I'll take a look around that forum too =)
Jul 04, 2014, 06:31 AM
Boaters are nice people.
Hi Tom,

Rule of thumb is to have the end bearing (=front of the prophub) between 10 and 13% of the hull length from the transom.

As a single prop boat suffers from propwalk, position the rudderblade next to the prop to counteract that.

In my boats, I also offset the entire drive train 4-5mm to the right to counteract propwalk, but not all (race) boaters are of the same opinion on that subject, it works for me though.

As race boats run around an oval with only right hand turns, the fact a single prop boat will turn much narrower to the right than to the left (propwalk again), isn't really an issue, as a result these boat have just the one turnfin, on the startboard side.

Regards, Jan.
Jul 15, 2014, 09:28 PM
Registered User
micromodder's Avatar
Hello everyone.

Lately if found a new addiction with small speedboats.Now I have 3 hulls of a very similar design that are setup for surface drive but use a small 2 blade prop under the waterline.I was just trying to make my own metal upgrade props, but any increase in prop diameter breaks the water surface.Id really like to sort this issue out just to learn.Since I'm capable of making brass parts or patching the plastic hulls I wanted to gather some opinions.All input is apreciated.

What style props should I persue?I noticed real surface drive off shore boats have up to 5 blades on the prop.Do the extra blades help reduce cavitation or something?

Which side of the prop should I try moving my rudders to?I'm guessing the side my prop is rotating towards so propwash hits it and counteracts?

Also what about shaft length for my props?Are there any rules or principals?

Here's a picture of my test boats transom with one of the props I made installed.


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