atomic-4 speed and stress

[tpalmer]

I'm trying to plan my first extended cruise. What is an expected speed of an ariel with an atomic four? With a 15 gallon gas tank how far could I expect to motor? This engine seems bullet proof, when do you begin to stress the engine beyond normal usage?

[marymandara]

With an old tired A4, figure your consumption at a gallon an hour and then be happy if it works out better. Because of the slope of the tank it is very difficult to guage by eye or stick.

The aperture shrouded prop is not the most efficient by any means...so your speed will probably top at about 5 Kt. . Watch your speed over ground on the GPS, you will find that at a certain point more throttle begins to mean less and less. Make a mark with a piece of tape to remind yourself where the throttle position was for max. efficiency, and call it good...least that's how I did it while the Commander still had an inboard. I wouldn't worry about "stressing" the engine...it's not like you are going to be running it wide open. These engines were intended to pack a much heavier load than an Ariel. FWIW, 3/4 throttle and wide-open throttle will yield about the same effect. 1/2 throttle is probably plenty. Don't worry about the speed too much anyhow..it isn't a powerboat!<G>

Dave

Dave

[S.Airing]

With my Atomic 4 I set the cruise power at 1200 RPMs(using about 9 horse power of the engine ) which gives me full hull speed in most conditions.At this setting Sirocco burns less than 1/2 a gallon an hour and thats with charging batteries.But the engine was over hauled in 92.

[Ted]

I'd say the 1/2 gallon an hour is accurate -- both before and after my rebuild in 2000. And I set my throttle somewhat like Mary does - by the point of diminishing returns. I find that there is a 'magic' point perhaps a knot or so below hull speed where the engine seems to be just loping along (still lots of throttle left that really increases speed) and the vibration and noise are minimal.

To make sure I never run low on fuel, I use a two tank system. I use a standard 3 gallon plastic outboard tank alongside the main tank. I have a valve in the cockpit that allows switching tanks so before I go out I can run off each tank for a few minutes. Both go to the switch, to a Racor water separator/fuel filter, and then to the engine. When I cruise, I let the main tank go dry an know I still have about 6 hours of engine time left. The extra fuel line and extra tank also provide backup should anything fail in either system.

Who is using what props? Next year mine needs a bottom job and I was thinking of replacing the prop with one of the two advertised in Good Old Boat -- the $275 3 blade from Indigo Electronics or the PerfectPitch Prop from CDI. Is there an agreed upon 'best' prop? Mine is ancient, but still move the boat!

[tha3rdman]

Figured I'd hijack this thread, since the last post was about props.

When I come into dock (double slip I'm on the right) I come in at a creep, just enough that the rudder still functions, when i use revers to slow down it walks horribly to the left (away from the dock and tward my neighbor).

Just have a 2 blade, wondered if anyone else had that bad of walk, and if the 3 blade helps notably.

[Mike Goodwin]

It's not the prop , but the keel design . The straight , almost parallel to waterline keel does it on every boat. Cape Dory's do it, Morgans do it ,even educated fleas do it .
I had a Dr. offer me $100 (in 1981 dollars) if I could back his boat (Cape Dory) into his slip like my boat (Falmouth Quay Punt by Tom Gillmer) did .
I tried for hours and it just wouldn't do it .
Posed the problem to Gillmer when I was in Annapollis and he showed me with half models.
My boat had a lot of drag to keel ( sloped upward quickly from rudder ) so the boat pivots on the point at the end of the keel .
Blue Moon would go wherever I pointed the rudder.
Straigth keels try to pivot on a point along the lower edge of the keel several feet in front of the rudder , so they don't respond to the helm , then all of a sudden they over-respond and the stern marches off to port or STBD ( depending on if you are gas or diesel ).
With #45 , I ended up lashing the tiller with bungie cord and steering with the outboard motor, which was better , but no cigar .

[c_amos]

FWIW.... (and drifting more off topic) I articulate the outboard WHILE I steer with the rudder. I believe that the ability to vector the thrust on either side of the keel helps alot, and the rudder grabbs pretty well when there is any sternway on.

(2 more cents) :rolleyes:

Not that I have an A-4......

[tha3rdman]

So what your saying is I have it as good as it is going to get, with out the water tank in the bow 97 is listed aft, (which would give me something of a pivot point) but once I level her back out it's definatly not going to get any better.

The only way I can back her is to drive it rally (rally racing) style, steer hard ahead of time and straighten out before you think you need to, just go with the drift, just hope you straightend it out in time or as you said "WEEEE" "Watch the BOAT watch the BOAT, the DOCK the DOCK!!" "they didnt need that pyling anyhow, or those nifty landscape lights on top the dock powerbox"

[Mike Goodwin]

To me , backing control is the weakest point of the boats . So I just docked facing in and backed out in a circle ( looked intentional too ) It was a common design flaw from the '60s for many boats.

[mbd]

Going from an ODay 22 with an outboard off the back, which would pivot on a dime, to the much heavier Ariel with an inboard was an eye opener. Mine has a deisel and a three bladed prop, and I can say I don't have the significant prop walk 3rdman mentioned. But the boat backs like a pig -- at best.

I was fortunate last season in that my slip backed up to a mooring field with plenty of room behind me, and room enough between me and the freshly painted and refurbished Cape Dory 27 next door (thank god!). Depending on the tide (current) and the wind, I'd give a good push away from the piling at the stern, goose it to get some momentum, then wait until the bow cleared the dock (fending off when necessary), then turn the rudder hard over depending on which way the bow chose to point, and throttle up to get steerage and hopefully clear the boats, docks, pilings and what have you...

I'm looking forward to getting back on a mooring soon. :)

[Robert Lemasters]

I found that I have more steering control with the rudder centered and secured using the outboard for steering. At very low speeds the rudder is almost useless, very slow response to the tiller. The Nissan 6hp four stroke with the prop I had modified per Mike has more than enough power and control for this boat even at low speeds. I seem to be able to back in to the slip a little better than going in forward.At about 3/4 throttle the boat reaches max speed and fuel economy, which is very good, less than 1/2 gallon per hour it seems. The long keel, tides, wind, and other factors has put me on edge docking when going out by myself. I hate it when someone dings my boat and I have respect for other people's boats. I wish that I had the time to put out a mooring, it would make single handing easier. :o