I have been asked to explain some of the observations I reported in this thread.
Some asked if perhaps my observations were overly optimistic, other suggested that my comments may be just off the wall. LOL. Let me assure you - it wouldn't be the first time! But in this case I must say:
au contraire. So far, I don't think I exaggerated much of anything. Let me summarize what I think the important points are.
I think I made the following three (3) major claims regarding the benefits of those new MEGA fins:
- Improved reverse
- "Power steering" effect
- Reduced stress on steering linkages
Speaking strictly for
myself (no relation to Jeff,
@Cobra Jet Steering LLC ).
1. Claim: Improved reverse
(enhanced steering in reverse and enhanced "breaking"/stopping power)
EXPLANATION
That one is pretty easy - the MEGAs simply focus the reverse jet. The way it works, the reverse thrust is generated by the water "escaping" through the bottom opening in the steering nozzle - when the central/main/back opening of the nozzle is enclosed by the buckets (dropping down).
That water (streaming out of the bottom of the steering nozzle) disperses quickly as it lacks much of any direction. It does shoot backwards somewhat but there is nothing to "channel" or focus that stream.
The MEGAs do that! - the PAIRED MEGAs focus water coming out of the bottom nozzle in the reverse direction, with a slight built-in toe-in alignment.
In other words,
without MEGAs that water disperses quickly but
with MEGAs (mounted on both sides of the bottom nozzle/opening) water shoots back more directionally and the thrust is substantially enhanced (in the reverse direction).
The total force of the water molecules/energy is of course unchanged, but the vector of their movement is.
(The main fins - MAGNUMs - don't do that as they are positioned further back: MEGAs are sticking forward, MAGNUM are sticking backwards - of the steering nozzles)
So - the bottom line is
with the MEGAs there is more push in the reverse direction. Therefore, faster reverse and more "breaking" (stopping) power.
Verdict? I think that claim is legit...
As an aside (and a bit of trivia) and another way to think of this question is in terms of principles of hydrodynamic focusing.
Two Stanford professors, Len (Leonard) Herzenberg and his wife Leonore, who were responsible for developing a technique called "flow cytometry" (a mainstay of modern blood cell diagnostics) used to explain the principle of hydrodynamic focusing in the following way (back when - when I was hanging out with them):
Len would simply point out that hydrodynamic focusing also provides the mechanistic basis for men being able to urinate while standing (generating "stream in the air"). True story. It was too funny.
But back to Cobra fins...
2. Claim: "Power steering" effect
EXPLANATION
The MEGAs stick forward of the "pivot" or axis defined by a line connecting bolts that attach the steering nozzle to the venturi nozzle. Water forces pushing on the MEGAs thus counteract the forces pushing on the MAGNUMs (which are sticking backwards of the "pivot").
In other words - if the line between steering nozzle mounting bolts is the "fixed hinge", or fulcrum, the MAGNUMs become the long(er) arm of the lever and the MEGAs become the short arm. The force of water pushing on the short arm (MEGA) offsets the force needed to turn/push the long arm (MAGNUM) against the water (when driving forward and turning the steering nozzle).
Hence - "power steering" effect or "power assist".
Of course this is
not the same mechanism as in automotive power steering, but it is a steering
assist nevertheless. Jeff likes to call it "power steering". I don't see anything wrong with that.
Verdict: I think that claim is 100% legit.
3. Claim: Reduced stress on steering linkages
EXPLANATION
This one is a bit more nuanced.
There is no question the MAGNUMs (deployed down at speed) will put additional force/strain on steering linkages in turns (as compared to riding with no fins) as they function essentially as a rudder - which is a good thing.
In this regard, adding a smaller, forward facing MEGAs (positioned on the other side of the "fulcrum") helps balance the larger MAGNUMs - relieving some of that additional pressure on the steering linkages.
Still, MAGNUM and MEGA (on both sides of the "fulcrum") will add lateral force on the pump in a turn (due to centrifugal forces of water molecules - in outward direction). Should that be a concern? I don't think so! - even though there is more lateral force on the pump - that's just like a skeg in an outboard motor lower unit. The pumps' transom mounts must be strong enough to push the boat - if those little fins compromise jet pump mounts I would say one has larger issues to deal with.
As far as the steering linkages themselves, to put this in perspective, Yamaha steering cables seem to last about 10 years on average before they need to be replaced - fins or
no fins.
I
personally think that those cables break primarily due to internal corrosion, more affected by water intrusion than usage, but more stress is probably not helping. And here - the MEGAs really help the larger fins - reducing the stress on steering linkages.
Verdict: So, this claim is also completely legit, IMO. Albeit fins by definition put more force on the steering linkages, the MEGAs (or any FANGs) offset that force.
Additional points:
- In case of an impact, the fins' mounting brackets are the sacrificial (softer) part which "gives" during an impact. Those are easily fixable at home. But at any rate, the articulating keel reaches almost a foot lower than the fins so damaging the hull and the new factory rudder is more of a concern, fins or no fins.
- MEGAs do not make the boat turn in any unexpected fashion. In fact, I find the steering to be a lot more controlled. It is predictable and also very sharp - like a race car.
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