2012 Return Run to the Vineyard

[ndutton]

Does anyone have information as to what is minimum acceptable pressure?

Disclaimer:
This response is based on what I think, not what I know.

I'd say any pressure capable of filling the carb bowl will do as long as it keeps up with your consumption. At slightly less than a gallon an hour it isn't much. Since the pressure reduction is past the tank draw and filter I think you're over the hump where pressure (or vacuum) is needed. A polishing filter could be an issue though.

I've been working with another listmate on an automatic fuel bypass system (concept complete, parts purchased but not yet installed) that is expected to drop the pressure at the carb to 1 psi. We will see how it works and post the results.

[Dave Neptune]

Preassure

Hanley, 2 psi should be fine. As I recall the supply preassure for the zenith is from 1 1/2 ~ 4 psi, it doesn't take much to pump a gallon an hour. You would be beter off with low preassure than to much. My mech pump works at around 2 1/2 ~ 3 psi and I have no starvation issues. If you wind up needing a bit more preassure, which I seriously doubt, plase a restriction as near the "tee" as possible and that should divert a bit more preassure to the carb.

Have you thought about the return stirring up the tank when the fuel is low? This could get the tank cleaned out a bit but carry a couple of extra spin-ons!!

Dave Neptune

[hanleyclifford]

Have you thought about the return stirring up the tank when the fuel is low? This could get the tank cleaned out a bit but carry a couple of extra spin-ons!!

Dave Neptune

The tank I am using as the "working" tank is the original which has a bottom drain - it has the best shot of being the cleanest. But I will have extra filters (all types) on board. I do have complete pressure adjustability with the ball valve in the return line.

[hanleyclifford]

Still over propped?

1000 rpm 13.5 vac
1200 12.0
1400 9.5
1600 7.5
1800 3.5
Tied to the dock. Comments?

[Marian Claire]

Hanley: Based on what I have read if properly propped the A-4 should turn 2400 to 2500 rpm with the direct drive and 3000+ for the 2 to 1. Remind me of what your set up is, prop/reduction etc. Dan S/V Marian Claire

[High Hopes]

I find a lot more useful boatthingy stuff here - http://www.mcmaster.com

Awesome site! Thanks!

[Dave Neptune]

Huh

Hanley, your lugging. When I was using trhe prop I sent you I could get 1700 at around 6" of vac and very little more if I cranked it. Now with the Indigo I get 10" and just over 1800 rpm's.
With your 2:1 box I should think you would be around 10" at 2400 and max cruise (7" or so) at 26~2800, these are guesses but should be close if you were proped for around 3,000 at WOT. You will gain a few RPM's when not tied to the dock but not much more than a few percent, say less than 10%.
When all is clean and well I cruise at 8" @ 2200 RPM's with the Indigo.

Dave Neptune

[hanleyclifford]

Dave, I think you're right. Maybe too long in the slip or still too much prop. Wish I had data from the trip south. Prop is at 13x11.5, 3 blade power boat prop. What do you think about 13x10 for the prop you sent me?

[Dave Neptune]

Prop

Hanley, you are lugging with a 13X11.5x3 blade. The 13x10 is it also a 3 blade or is it the cut down 14" with questionable pitch I sent you. Big change 2 to 3 blade! You say you are using a power boat prop, do you have any pics? I most cases the blades are simply wider for absorbing more torque supplied by larger power plants.
I remember you ran the one I sent you and you thought it needed a bit more pitch as it was spinning to fast. Do you remember the vac load at around 2500 RPM's, or anywhere on the rpm curve? Blade area plays a big part of the equasion, you need enough to absorb the torque and any more is just wastin' power for the additional friction.
Personally I would run with to little and let it spin a bit but not over-rev the beastie. The insides of the engine will be much happier and the losd off the bearings is a bunch.

Dave Neptune

[hanleyclifford]

Dave , The other prop is the one you sent me. Before sending it out to the shop I am trying to zero in on exactly what I want. Changing the 3 blader from 13x13 to 13x11.5 made a huge improvement for me but the prop you sent me allowed 3000 rpm way to easily...trying to find the sweet spot...

[Dave Neptune]

Another thought!

As a comparison, when I first installed the Indigo on my boat and started down the fairway I though this thing is to small because I was using a lot more RPM's but the manifold load was staying very light. When I got out to the harbor and started to apply power she spun right up to where she was supposed to. This was such a departure from what I was using and had tried that I really didn't like how it was working, "I" wasn't accustomed to it yet. Well that lasted about 2~3 trips and I started developing my new fuel usage curve with the Indigo spinnig 25% faster than anytyng I had used. The big suprise was it was using far less and the intermediate settings and a bit less at the same a "cruising speed". The engine was much happier and after getting myself accustomed to the broader RPM range I luv it!!!!!!!!!! It works well extracting about everything this ole' A-4 can deliver with the direct drive.
Thought this may eleviate some of your concerns.

ave Neptune

[hanleyclifford]

Brain Wobbling

Dave, Right now I am thinking of having your prop taken to 13x10 or 13x11. What do you think?

[Dave Neptune]

Decision

Hanley, you need to decide which you want to go with a 2 or 3 blade.
The 3 will give a bit more bite for a headwind and sea if you get the proper RPM's, however it will drag much more when sailing.
The correct 2 blade will work almost as well in the headwind if you get the same RPM's at full throttle and be a bit freeer running through the rpm range. The big advantage is sailing you can hide the prop for a considerable decrease in drag and more sailing speed .
The 2 blade will require a tiny bit more pitch than a 3 if you stay with the same diameters.
Blade area plays a big part and I'm not to sure about your PB prop configuration.
Decide where you want the engine to run RPM wise for your cruise and work to it. When you get it you'll be very satisfied with the results.

Dave Neptune

[Dave Neptune]

Check?

Did you evr get the prop I sent measured for pitch? Taking it up 2" from where it is may be about right. I also think the cut down prop like I sent you will work well because the blades are a bit wider that a 13" off the shelf.

Dave Neptune

[hanleyclifford]

Moving cautiously

Dave - In view of the fact that the 2 blader needs a little more pitch than the 3 blader for the same "bite", I think I'll go to 13x11 with the 2 blader since I only want to pick up 200 rpm or so. I cruise at around 1900 now with decent gas mileage.