"Long Leg" Sterndrive?

[myoldboat2]

Does anyone make a "long leg" lower unit that fits a # 1 Mercuiser upper unit, or a long leg upper+lower replacement?

 

[JustJason]

Re: "Long Leg" Sterndrive?

Nope, no such thing. Whats the problem with yours? Pic's would be great.

 

[myoldboat2]

Re: "Long Leg" Sterndrive?

It's on a pontoon boat and the pontoons extend rearward, so the turning isn't as effective as I'd like. Lowering the engine and sterndrive looks like a huge undertaking (new bilge, new transom, ...). I'd just like to get the prop centerline 3 to 6 inches lower.

 

[myoldboat2]

Re: "Long Leg" Sterndrive?

Not the best pic, but this shows the general setup. The prop centerline is near the bottom of the pontoon logs. I think some of the propwash gets deflected backward by the toons when turning.

 

[Howard Sterndrive]

Re: "Long Leg" Sterndrive?

ask a local propeller shop about adding some "cup" to your prop.

I think that would be worth a try

 

[JustJason]

Re: "Long Leg" Sterndrive?

Is that rig factory or did some previous owner do a hack and slash special?

Cupping may help... may want to talk to a welder about having a skeg extension welded on.

 

[myoldboat2]

Re: "Long Leg" Sterndrive?

Factory rig -- Harris FloteBote.

A skeg extension, hmmm... I was thinking that more propulsion sideways is what is needed... you're saying that a larger skeg to provide more area to force the turn, is that right? I wonder how much of the turning force comes from the propulsion being to the side and how much from sticking the angled sterndrive & skeg into the slipstream. Anyone know?

Good thought, thanks.



.

 

[JustJason]

Re: "Long Leg" Sterndrive?

It all depends on the boat and how the flow of water is hitting the drive. The drive is a rudder, the skeg is the bottom half of that rudder. Want to turn better... you need a bigger rudder.

 

[myoldboat2]

Re: "Long Leg" Sterndrive?

I'll look into having the prop cupped, Howard, thanks.

Jason, I'm going to look into a skeg extension. Maybe one of those bolt-on jobs.

Thanks guys.

 

[myoldboat2]

Re: "Long Leg" Sterndrive?

Started thinking about increasing the sterndrive rudder size. Figured I'd start by comparing the profile of the drives in the family:

It looks to me like the Bravo line has rudders of big area due to the "fin" of the whole lower unit being extended forward. That makes a lot of sense to me, because you get the increased rudder force without extending the skeg deeper into the water.

For my I-Drive (sorry about the lousy pic, it's all I could find), I guess I have three options, with some concerns:

Option 1: Extend the lower unit "fin" forward; concerns -- welding will heat up that whole case and I don't want to tear it down; not sure a "fin" could be bolted around the case; concerned about the strength of the case

Option 2: Extend the skeg forward; concerns -- how? I haven't found that type of bolt on skeg guard and would rather not deal with welding; how large is too large?, i.e. how much increased skeg-rudder load can the case safely carry?

Option 3: Extend the skeg down; concerns -- hitting rocks, although I don't draft much depth; how? I haven't found that type of bolt on skeg guard and would rather not deal with welding; how large is too large?, i.e. how much increased skeg-rudder load can the case safely carry?


Does anyone have any experience with this, or thoughts about it, or want to just make fun of me even thinking about this...?

Thanks in advance.

 

[myoldboat2]

Re: "Long Leg" Sterndrive?

btw, I also have one of those bolt-on anti-cavitation plates mounted on the drive. Maybe I could run some stock aft along each side of the plate and bring them together to support a rudder fin that is behind the propeller, but has its plane vertically inline with the center plane of the drive. This would swing further out when turning and transfer the loads into the bolted joint between the lower and upper units, which is a pretty strong section. As long as I have the clearances, I could make a reasonably sized fixed aft rudder plate. And I wouldn't be messing with the drive itself. On the other hand, the propwash directly behind the prop probably wipes out any of the normal slipstream, so I may not get much turning force at all. Maybe use a similar plate, but swung in front of the drive. That would also move the "center of pressure" forward and reduce steering wheel forces. Thoughts?