Areneson on a 27ft Uniflite?

[big-boss]

What about an Arenoson on an old Uniflite? I am repowering one and thinking of a Cummins/ ZF trans @ 1.5:1 and an Arenson No. 6. Am I on the right track? Thanks

[marshmat]

Uniflite 27.... this one?
http://www.unifliteworld.com/models/27express.html

I suppose an Arneson conversion would be possible. But this doesn't strike me as the kind of boat that would benefit from a surface-piercing prop.

Can you provide any more information on the boat?

[big-boss]

That is the one. 27ft Express, 1970. Mine has been in restoration for the last 14years is completly cleaned and apart and ready for a new life. Hull No. 53
I was thinking of the surface not for speed but for effiency in the baots design speed range. WHich I do not realy know what they are only have experiences from other owners. Cruse 12 to 16knots, with toip speed somewhere in the mid twenties. I have to start from scratch anyway. I like the boat and it is something I can trailer if I need to.

[Steve H]

Is this project going anywhere?

[big-boss]

Yes, I have the Surface drives. Only going to use one behind a nice 6bta 300HP +/-. Slowly but surley. Do you think it will work OK?

[Commuter Boats]

I would think you would get better performance and lower maintenance if you went with a ASD 8, and more gear reduction which would allow you to spin a larger diameter propeller.
Gerald

[Steve H]

Do you have a prop yet?

[Commuter Boats]

Originally Posted by Steve H

Do you have a prop yet?

Steve, I sent a private message.

[DanR]

Originally Posted by big-boss

What about an Arenoson on an old Uniflite? I am repowering one and thinking of a Cummins/ ZF trans @ 1.5:1 and an Arenson No. 6. Am I on the right track? Thanks

I’ve had over 600 hours running a surface piercing drive on a 32 ft boat, and one old saying sums up my experiences. “When it was good, it was very very good, and when it was bad, it was horrible (expensive!!!)”. I had twin Yanmar 315s connected via Hurth 630s at 2.53:1. My shafts were 1.75”, AQ22, and the props 24X22 from Osborne Propellers in Vancouver, BC. Fully loaded (about 15,000 lbs) I could run 36 knots, slow down to 28, and I only burned 17 gal/hr total for both engines. That’s the good, now the bad. I broke 2 shafts the first year, in nearly flat calm water (AQ19); a high quality flex coupling broke the second year, and maneuverability in reverse was an embarrassing experience (prop wash strikes the stern making things really squirrelly). Rough water operation was challenging, she didn’t want to stay on step at lower speeds, and the props would fully submerge, greatly loading the engine. (Not as much of an issue with an Arenoson if you trim them up, and down, and up, and down) You need a high torque engine to handle the load as the prop submerges. Both engines were replaced at just over 600 hours, one damper and a bell housing were cracked and that transmission also was replaced. I can’t say enough good things for Osborne Propellers, they have lots of experience with various surface piercing drives and helped solve my shaft issues. They suggested I change from AQ19 to AQ 22, and use splined in lieu of keyed shafts. Osborn also explained that addition to the irregular torque, the shaft also had a bending moment as each blade struck the surface of the water. In summary, I won’t use surface piercing again, the issues aren’t worth the extra 2-3 mph, and a little less fuel. (IMO). I wish you better luck than I had.

[Frosty]

What you experienced is pretty much life with surface drives. Reverse can be improved with reverse plates directing thrust under the boat.

Your shafts are way too thin. Yes the shafts push from one side due to half the prop in the water, I use 2 inch with the 630A with 250 Hp, 24x24 seafury's

Gearbox and bell housing probs is not a result of your surface drives, but possibly the result of the shaft size and misalignment.

Yes the torque is irregular as you put it as thrust is by the blade in the water, multiple blades cure this, did you have a 3 blader?

Surface drives are for planing only.

[Steve H]

I assume you were using fixed shafts. Did you design and install it, or was it existing?

[Frosty]

I designed and made them yes. 7 years ago. They are fixed shaft 4 foot long 8 degree down ZF 630 a.

They are very different to conventional but ive grown to like them being very smooth.

Ive got over reversing probs by the method mentioned above, it is now acceptable and steerage in reverse is normal.

Mine are shallow, the tips of the blades are only 3 inches below the water line at rest, I dont get bog down at all, and I dont use exhaust outlets to free them.

[TollyWally]

Frosty,
Would you mind posting some pictures or drawings of the system you designed and built? I find this stuff fascinating.

[Frosty]

Get a load of this thread, pics in here, but rudder heavily modified since then, infact they are now one legged.

Shafts thru the transom?

[DanR]

Originally Posted by Frosty

What you experienced is pretty much life with surface drives. Reverse can be improved with reverse plates directing thrust under the boat.

Your shafts are way too thin. Yes the shafts push from one side due to half the prop in the water, I use 2 inch with the 630A with 250 Hp, 24x24 seafury's

Gearbox and bell housing probs is not a result of your surface drives, but possibly the result of the shaft size and misalignment.

Yes the torque is irregular as you put it as thrust is by the blade in the water, multiple blades cure this, did you have a 3 blader?

Surface drives are for planing only.

The original shafts came with the drive from Simplicity-Marine, and I use 4 blade cleaver props. I’d be happy to discuss my experiences with Simplicity Marine, but by direct email only.

When I speced the replacement shafts I trusted the calculator on marinediesel.com. It’s a good site for engines, but there’s not a lot of experience with surface drives. Their calculator showed a huge safety margin with 1.75 AQ 22 shafts using the 2.53 reduction. Perhaps that works for standard props, but as you said, insufficient with surface drives.

Over 3 years of running the boat I discovered a couple of tricks to help docking and maneuverability in reverse. The first was by accident, after a shaft broke, and I couldn’t locate right hand replacement prop. I used 2 left hand props for the rest of the season, and boy could I swing the stern around, but only in the direction she wanted to go.

The second “trick” came from a boat handling site on the net which was discussing twin engine handling techniques, and how to “walk” a boat sideways. They recommended changing prop rotation to spin outwards when moving ahead, and inwards in reverse. To “walk to port” from a dead stop, put the helm hard to port, the port engine in forward, and the starboard engine in reverse. Prop wash on the port rudder will want to turn the bow toward port; however, reverse pull from the starboard engine will want to swing the stern to port. To walk to starboard, just reverse the operation. It took lots of practice in a private isolated cove, but I finally got it down. I don’t know why changing prop rotation helps this maneuver, but it does.

A couple of final comments about maneuverability, especially with fixed drives such as Simplicity: When on step, only a very small portion of your rudder is in the water; directional change requires substantial helm movement, or use of your trim tabs. Also, lateral trim, ie passenger movement, affects direction; you’ve got to be alert.

This boat is like a high maintenance woman; she needs lots of care and attention, but is wonderful when things are going right.