i have a catalina 30, with a atomic 4, that motors at 4.5 knots max. my friends sailboats cruise at 5-6 knots. they have longer boats, with larger keels, but with less horsepower. i thought it was all the gear i had for cruising but now that it is off it is still maxing out at 4.5 knots. under sail the speed is fine, but id like to be able to keep up when motoring. any help would be appreciated.
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It's the same story- prop pitch
The A4 should run at 3000 rpm at rated horsepower. If you can turn more than, say 3300-3400 rpm then your prop probably needs to be bigger. Bigger could be in diameter(if you have room to swing it) or in pitch. I had an A4 (with direct drive) on my 30' Morgan and had a low motoring speed with a 12x6 2-blade prop. I changed to a 12x7 and picked up some speed. I wish I could give you the particular details, but this was 15 years ago.
The A4 should run at 3000 rpm at rated horsepower. If you can turn more than, say 3300-3400 rpm then your prop probably needs to be bigger. Bigger could be in diameter(if you have room to swing it) or in pitch. I had an A4 (with direct drive) on my 30' Morgan and had a low motoring speed with a 12x6 2-blade prop. I changed to a 12x7 and picked up some speed. I wish I could give you the particular details, but this was 15 years ago.
motoring
thanks for the reply, rich. i thought it could be the prop. not sure if i should go with a larger two blade or go with a three blade?
thanks for the reply, rich. i thought it could be the prop. not sure if i should go with a larger two blade or go with a three blade?
Based upon my experience with a 3-blade
I would go with a 3-blade if you are willing to suffer the drag. I never had a 3-blade on my A4 but on my Hunter it is great! But be sure to check the rpm so you get the corect prop. Like any other marine engine, you don't want to lug the engine. A good prop shop should be able to tell you exactly what props to use based upon your hull shape, displacement, engine, and transmission drive ratio.
I would go with a 3-blade if you are willing to suffer the drag. I never had a 3-blade on my A4 but on my Hunter it is great! But be sure to check the rpm so you get the corect prop. Like any other marine engine, you don't want to lug the engine. A good prop shop should be able to tell you exactly what props to use based upon your hull shape, displacement, engine, and transmission drive ratio.
Motor Slow, but how does it Sail?
Another thought on this (in addition to my thoughts on the Ask a Catalina Owner Forum): How does it sail with respect to your buddy's? Will she sail over 4.5 knots? That would be a dead giveaway that there is something going on with your drivetrain - prop or engine rpm, etc. If she sails close to hull speed in a nice breeze, then something is wrong in the mechanicals. If she sails about the same speed as when you motor, then start as I suggested and check your bottom, (as you suggested) how much stuff you are carrying, the calibration of your knotmeter. Note that while a 3 bladed prop might seem like a good idea - for a motorboat - remember that you are a sailboat and that 3 bladed prop is added drag (read slower) under sail. Good Luck! Tim Brogan April IV C350 #68 Seattle
Another thought on this (in addition to my thoughts on the Ask a Catalina Owner Forum): How does it sail with respect to your buddy's? Will she sail over 4.5 knots? That would be a dead giveaway that there is something going on with your drivetrain - prop or engine rpm, etc. If she sails close to hull speed in a nice breeze, then something is wrong in the mechanicals. If she sails about the same speed as when you motor, then start as I suggested and check your bottom, (as you suggested) how much stuff you are carrying, the calibration of your knotmeter. Note that while a 3 bladed prop might seem like a good idea - for a motorboat - remember that you are a sailboat and that 3 bladed prop is added drag (read slower) under sail. Good Luck! Tim Brogan April IV C350 #68 Seattle
RPM / Prop
What you need to do is note the cruising speed and the max engine RPM. If the engine is turning up what it's supposed to ( RE:3000 or whatever it's max output is rated at ) then you need to find out what prop you have on the boat. Next step is to find a GOOD prop shop in your area. They will be able to tell you what you need to do. But if you go in there without knowing your max RPM, and your current prop you are wasting time. These are the two constants.
What you need to do is note the cruising speed and the max engine RPM. If the engine is turning up what it's supposed to ( RE:3000 or whatever it's max output is rated at ) then you need to find out what prop you have on the boat. Next step is to find a GOOD prop shop in your area. They will be able to tell you what you need to do. But if you go in there without knowing your max RPM, and your current prop you are wasting time. These are the two constants.
Talk to other C30 owners
All the advice so far is good but before you trust a prop shop to make their best guess at what you need talk to other owners of your boat and engine to find out what works for them. That approach solved a similar problem for me. There must be a Catalina web site you can access. BTW, don't be scared off from going to a 3 blade. I now have one and the extra speed and power for motoring is great, and I have never really noticed any hit in sailing performance. Kevin
All the advice so far is good but before you trust a prop shop to make their best guess at what you need talk to other owners of your boat and engine to find out what works for them. That approach solved a similar problem for me. There must be a Catalina web site you can access. BTW, don't be scared off from going to a 3 blade. I now have one and the extra speed and power for motoring is great, and I have never really noticed any hit in sailing performance. Kevin
Thanks for the replies. I did all my testing with a freshly cleaned bottom, using a GPS, and without a current/wind. The boat sails great reaching maximum hull speed, well over the motoring speed. The only thing I can think of is either the motor isn't making maximum RPM or the prop is hindering the engine performance. I don't have a RPM guage, but I just gave the engine a full tune up. I will make sure the engine is making maximum RPM though, before I spend the money on a prop. Thanks again Ethan
Catalina 30 with A4 and 2 bladed prop
I just hauled my C30 TR with Atomic4 on Monday. After 2 years in the water, the two bladed prop produced no thrust so I had to get towed to the lift. The prop and shaft looked like popcorn balls were growing on them but bottom was clean due to good anti foul paint from 2 years ago. Once pressure washed nthe shaft and prop, scraped the residue from barnicles off the prop and bottom sprayed clean (total of 45 minutes). I easily made 4.5-5.0 knots on the way home at about 66% throttle (no RPM Tach so I go by sound). There was more throttle there, just felt comfortable at 4.5 knots. This has been the norm after a hull cleaning for me. That is a lot of mass to push through the water and I never worry about keeping up motoring it is sailing that tells the tale.
I just hauled my C30 TR with Atomic4 on Monday. After 2 years in the water, the two bladed prop produced no thrust so I had to get towed to the lift. The prop and shaft looked like popcorn balls were growing on them but bottom was clean due to good anti foul paint from 2 years ago. Once pressure washed nthe shaft and prop, scraped the residue from barnicles off the prop and bottom sprayed clean (total of 45 minutes). I easily made 4.5-5.0 knots on the way home at about 66% throttle (no RPM Tach so I go by sound). There was more throttle there, just felt comfortable at 4.5 knots. This has been the norm after a hull cleaning for me. That is a lot of mass to push through the water and I never worry about keeping up motoring it is sailing that tells the tale.
Clean prop
I was amazed at how much difference a clean prop makes. A few barnacles is all that it takes to kill your speed.
I was amazed at how much difference a clean prop makes. A few barnacles is all that it takes to kill your speed.
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