bad porpoising 3100
05-18-2006, 01:44 PM
#51
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Re: bad porpoising 3100
Originally Posted by ROTAX454
Can the stern lift (excessive) be controlled with some prop modification rather than changing the rotation?
05-18-2006, 06:40 PM
#52
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Re: bad porpoising 3100
Originally Posted by Dueclaws
Sean-
That's what fixed my Chris Cat. It wasn't porpoising from bow lift, it was "popping" the tail from too much stern lift from the props. John Tomlinson gave me the advice to turn the props in and it worked. Ran great to 125.
You do need to be more careful when turning the boat, since rotating the props "in" tends to make it lean out more.
Due
That's what fixed my Chris Cat. It wasn't porpoising from bow lift, it was "popping" the tail from too much stern lift from the props. John Tomlinson gave me the advice to turn the props in and it worked. Ran great to 125.
You do need to be more careful when turning the boat, since rotating the props "in" tends to make it lean out more.
Due
You are so right about rotating those props "in" on a cat. Turning takes much more concentration.
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05-19-2006, 08:04 AM
#54
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Re: bad porpoising 3100
The Chris Cat was powered by supercharged (low boost) 572's: about 800 hp each. The current owner Andy (Greencard) repowered with similar,but slightly smaller engines. Interesting: he used smaller diameter props (16.5"), which reduced the leaning of the boat when turning and had some other benefits. I had 17.5" diameter on the CC which tells me that I should've experimented more with props.
RE: "turning-in". Looking at your props from the rear. the port side prop turns clockwise and the starboard turns counter-clockwise: when in forward gear.
Sometimes reducing the diameter of props will reduce stern lift, but you'd need to ask prop experts like BBlades or ThrottleUp about that.
Due
RE: "turning-in". Looking at your props from the rear. the port side prop turns clockwise and the starboard turns counter-clockwise: when in forward gear.
Sometimes reducing the diameter of props will reduce stern lift, but you'd need to ask prop experts like BBlades or ThrottleUp about that.
Due
Last edited by Dueclaws; 01-08-2007 at 03:37 PM.
05-19-2006, 09:49 AM
#55
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Re: bad porpoising 3100
Top of the prop blades swing the direction of "in" to each other or "out" away from each other , forward gear. As for leaning and handling issues of turning props in that maybe a an issue on some hull designs. My Motion cats only leaned out on very slow turns (under 50mph) Even over 100 mph they would lean in slightly on a turn. My MTI does the same thing. Leans in real nice for high speed turns.
05-20-2006, 09:43 AM
#57
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Re: bad porpoising 3100
[QUOTE=Dueclaws]The Chris Cat was powered by supercharged (low boost) 572's: about 800 hp each. The current owner Andy (Greencard) repowered with similar,but slightly smaller engines. Interesting: he used smaller diameter props (16.5"), which reduced the leaning of the boat when turning and had some other benefits. I had 17.5" diameter on the CC which tells me that I should've experimented more with props.
RE: "turning-in". Looking at your props from the rear. the port side prop turns clockwise and the starboard turns counter-clockwise: when in forward gear.
Sometimes reducing the diameter of props will reduce stern lift, but you'd need to ask prop experts like BBlades or ThrottleUp about that.
Due[/QUOTE
Due, Thanks for the infor. Very helpful in setting up my 31 cat. For the time being, I will leave the turning out set-up and mix up the pitch vs. number of blades to get the right "feel" of the boat. Side note: Would trade my boat in a heart beat to have a shot owning a Jag. Beautiful boat. Hope to see you at a poker run some day. Maybe a Key West PR. Richard
RE: "turning-in". Looking at your props from the rear. the port side prop turns clockwise and the starboard turns counter-clockwise: when in forward gear.
Sometimes reducing the diameter of props will reduce stern lift, but you'd need to ask prop experts like BBlades or ThrottleUp about that.
Due[/QUOTE
Due, Thanks for the infor. Very helpful in setting up my 31 cat. For the time being, I will leave the turning out set-up and mix up the pitch vs. number of blades to get the right "feel" of the boat. Side note: Would trade my boat in a heart beat to have a shot owning a Jag. Beautiful boat. Hope to see you at a poker run some day. Maybe a Key West PR. Richard
05-21-2006, 07:08 AM
#58
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Re: bad porpoising 3100
Thanks for the compliment for the Jag.
Stay in touch! I'm famous for working years completing a project, selling it and then starting again: I enjoy the challenge ....drives my wife crazy
PM me anytime and I'll send you my email address.
PS: (this is my 9th project
)
Stay in touch! I'm famous for working years completing a project, selling it and then starting again: I enjoy the challenge ....drives my wife crazy
PM me anytime and I'll send you my email address.
PS: (this is my 9th project
)
Last edited by Dueclaws; 01-08-2007 at 03:37 PM.
05-21-2006, 10:42 PM
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Re: bad porpoising 3100
due, sweet ride! any more pix of it?
btw i ran today at my local lake in smooth to washing machine water and the ladies loved the stable ride. also ran against some different guys and 110mph was easy to achieve. still hit'n the rev limiters so im going to look for some 34p bravos and see.
btw i ran today at my local lake in smooth to washing machine water and the ladies loved the stable ride. also ran against some different guys and 110mph was easy to achieve. still hit'n the rev limiters so im going to look for some 34p bravos and see.
