Inline vs Offset Rudder in Catamarans at High Speed

[10gauge]

Is there a difference between inline and offset rudder assembly in 30-40" catamarans at high speed?... It would seem that an inline rudder would impede prop thrust from the rudder, and the offset rudder would be clear of the props wake. Has anyone measured or noticed a difference in performance between these 2 assemblies?...

Thanks

[Pedro Ramos]

personally i don't know the difference but for maintenance purposes the off set is better imo. you have a very valid question.

[Make-a-Wake]

Several years ago a friend of mine tried to calm his Geico Cat down from the bouncing, he added an offset rudder and it ran much better. So on the same hull the offset was better.

Stock Geico in first pic, second is the Mystic(same boat) in which they added an offset rudder from the factory

[10gauge]

Thanks Pedro and Make-a-Wake! I have a 34" M-1 Cat pictured with "slightly offset" and "more offset" rudders. I'm stuck with this Not-So-FineDesign HW. Needless to say, this was before I met Steve. The strut was too narrow for the 0.187" drive - unusable! So I ended up using an Aeromarine Strut (silver) with teflon bushings. The "slightly offset" rudder of the FineDesign overlaps one side of the prop -- I don't know how this will affect performance?... It would seem it might turn vigorously when you turn left (the prop overlap region).

Mounting the "more offset" SpeedMaster rudder clears the prop completely even with a x450, but it is not easy without tooling parts and reworking the transom to straighten curved surfaces. Even then, the space is limiited inside for mounting screws. The M-1 is a fast hull, but a nightmare to make versatile for altering HW.

Finally, the easiest option to mount on the M-1 is to use the inline rudder, for which it was designed. As you noted, Make-a-Wake, high speed stability is an issue.

[Make-a-Wake]

I would not use the blue one. His Geico was right at 42mph so its not real fast but it settled a 29" hull down at that speed.

[10gauge]

Thanks Make-a-Wake! That's what I'll do.

[madmikepags]

Inline rudder has your rudder always in your propwash and never "clean" water, off set ruder is the best and most consistent rudder setup. Yes the M1 is a pain in the as to work on, really nice hull but the Aeromarine Sprintcat is a better performing racing hull and much easier to work on.

[10gauge]

Thanks Madmikepags! Great to hear from you -- You've always given me great advice on RRR when I was setting up my first boat, the Mean Machine. Everytime I pick up the M-1, I wish I had known about the SprintCat prior. Your experience with the M-1 vs SprintCat was insightful several years ago and made me want to go in the SprintCat direction. I actually ordered a SprintCat with nitro layout and will experiment with my 1527/1Y and 1527/1.5D on 6S2P... Ultimately a x452 or x455.

Any links on how to detongue, and cup props?... I think that's the next step to achieve higher performance.

Thanks

[properchopper]

Just putting the finishing touches on the "Mr. Pags" edition/design SprintCat .

DSC06554.JPGDSC06552.JPGDSC06550.JPGDSC06558.JPG

[10gauge]

Properchopper, that's a labor of love! Thanks for the great pics! I like the dual-water pick up. I like how you have so much battery room without the rails. The Team Believer hull is also touted to have the same sponson design, but being 1/2lb heavier and 1/2" wider, I'm not convinced that T.B. can perform any better than the S.C.

I just ordered mine with 5" rails since I had an extra 5" rail mount (from my Phil Thomas 45 Hydro that I never built). I'll have to mount the batteries on top of the center and be attentive to layout to dial in the C.O.G. However, it seems I'll have to wait a few weeks to get it in red gelcoat from AM. I went with the Classic Cowl thinking that it might be more sleek for potential SAW experimentation at 8S... Off course, I'll have to read up on detonguing and cupping props.

[montymike]

Huuuuuummm I have seen style hull before...and cut out style tunnel.