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Alum cat running great into the wind, downwind not

Printed From: The Fishing Website
Category: General Forums
Forum Name: The Boat Shed
Forum Description: Discuss all things boating.
Printed Date: 24 Sep 2023 at 9:05am

Topic: Alum cat running great into the wind, downwind not
Posted By: jules75
Subject: Alum cat running great into the wind, downwind not
Date Posted: 02 Jan 2023 at 3:50pm

I have recently built a 4.5m aluminium catamaran and have spent a lot of time testing to get the optimum set up for the motor height with a number of other modifications (extending the hulls, centre sponson).
I have been testing it in all sorts of conditions in a local river which is very wide. Into the wind and waves it goes like a cut cat (no pun intended) but when going down wind it (the motor) really doesn't like it. There are no waves to speak of just surface ripple.
I'm just wondering if anyone knows why this would be?? It will be creating lift going into the wind but I don't know why I can't get the same sort of performance (it's a fishing boat predominantly but wanting to do the occasion biscuiting with the kids) either way. Not that I'm looking for performance per se but just don't want the motor to bog down like it does depending on wind direction. Any help appreciated...

Posted By: Fish Addict
Date Posted: 02 Jan 2023 at 11:13pm
Good upwind and not so good downwind is a characteristic of most cats, including those with twin motors. As a previous cat owner, (twin motors) I found they can be brilliant in some conditions and not so flash in other conditions. It was certainly a learning curve driving a cat after previously owning mono hulls. Increasing the speed often resulted in a better ride. Try trimming the motor up and opening the throttle (sensibly of course) and see what happens.    

Posted By: Bounty Hunter
Date Posted: 03 Jan 2023 at 8:57am
sailors know it as 'apparent wind' 

- less pressure under the bridge-deck going down wind = less lift

No disintegrations!

Posted By: OneWayTraffic
Date Posted: 05 Jan 2023 at 7:13am
Got any more photos of the boat and build process? Some of us like looking at projects.

Posted By: Shambles
Date Posted: 07 Jan 2023 at 4:33pm
Hey mate,
I don’t have any answers to your question but have a 4.5m cat myself. If you’re interested in checking out my setup, or just discussing small power cats quirks, let me know. I have a few questions of my own. I think it’s a great platform though.

Posted By: jules75
Date Posted: 13 Jan 2023 at 11:07am
Here's a couple of photos of build etc

Posted By: jules75
Date Posted: 13 Jan 2023 at 11:10am

Posted By: jules75
Date Posted: 13 Jan 2023 at 11:12am

Posted By: jules75
Date Posted: 13 Jan 2023 at 11:14am

Posted By: jules75
Date Posted: 13 Jan 2023 at 11:20am
Hi Shambles. Yeah mate I'm very keen to discuss cats with you! Could you send a few photos on your other post of your minicat?

Posted By: jules75
Date Posted: 24 Jan 2023 at 10:36am
Update: I think I've nearly cracked it! Went for a run I the river yesterday at Foxton. There was a fair breeze blowing at times up and down the length of the river so it was good to test into the wind (optimum) full throttle and very quick again with lots of wind being pushed into the tunnel creating good lift. The runs with the wind behind us initially were frustrating because there was a noticeable difference in performance. I found opening it up to full throttle made it run better with the outboard liking it more. Still about 80% of the into the wind results but I was happy enough.The lower down revs not so much. Again more wind forced down the tunnel...Also this was the first time I tried the longer anti-cavitation plate that I made. I think it made quite a difference when trimmed up. The new plate extends around 100mm longer to the rear.
While we were there my kids and I tried out their new ski biscuit which went well too!

Posted By: smudge
Date Posted: 24 Jan 2023 at 4:54pm
Good work, you must have been a bit worried initially

Best gurnard fisherman in my street

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