TFL (HK) Genesis upgrade question

[Old School]

A local supplier has a Genesis upgrade kit to fit a 3/16" driveline. Part of the kit is a strut with a lower fin (below the strut barrel) to "improve stability". What is the purpose of this please? Is it to maintain straightline stability?

The reason I ask this is that I have a HK Libero and under full power, according to my son who was driving the boat, the hull appears to very slightly crabwalk to the right with no rudder compensation needed . I personally did not note this as I was more interested in the outright speed of this hull.

As the Genesis upgrade strut should be an almost direct replacement for the stock Libero strut (I am upgrading it to 3/16" driveline), I am wondering if the modified lower fin on the Genesis upgrade strut may "straighten" the boat under power. I have checked the alignment of the driveline to the hull and it appears correctly aligned. I know that fins are not normally fitted to hydroplane struts but if it improves straightline stability then I may consider this strut as part of the driveline upgrade. At present the boat tracks just fine and as stated I did not note the slight offcentre position of the hull under power.

My son's catarmaran hull also exhibits this tendency to shift the rear of the hull to the right under power as it lifts up on plane and then straightens up (he was using a high lift 38 mm 3-bladed prop). The shift is minimal but noticable.

[rol243]

the added fin to strut does help in a straighter direction of boat travel and has been used for many years on cat / tunnel hulls and mono hulls. if your hydro has a slight right crab you can adjust the turn fin very slightly if the fin has a curl on the base you can push the bottom of fin forward by approx 1/8 inch per test until the hull tracks dead straight.
with the cat hull you shouldn,t use a lifting prop atall as you want the nose to rise at speed not the rear, so try a non lifting prop and make sure its sharp and well balanced. try something like Octura 2 blade 440 / 442.

[Old School]

................................ you can adjust the turn fin very slightly if the fin has a curl on the base you can push the bottom of fin forward by approx 1/8 inch per test until the hull tracks dead straight.........

Many thanks, I never thought to associate the crabbing with the turn fin. I had set the fin up as per a diagram seen on the web with a vertical line drawn through the mount/pivot point slightly ahead of the lower forward edge of the fin.

As regards the 3-bladed propellor used on my son's cat, I immediately noticed that as power was applied the nose of the cat became very "heavy" (nose down attitude) producing a lot of spray until the hull was on plane.

[MadProps]

that strut fin will bleed off speed and if crooked it may be fighting the rudder
the Genesis likes the octura 45mm I tried the 40 and 42, Im currently de toungeing a 47mm to test next

[Old School]

Many thanks