New Propeller Problems

tsunami · 25 July 2001, 09:10

I run my boat a 7m Rib with a 225hp Suzuki with the original propeller that was supplied with the engine. That being a 14.25" x 22" pitch propeller.
Although the prop works fine and gives me a top end speed of 47 knots, I only get 5100rpm. For general use this wouldn't normally bother me. The problem lies in the fact that in just over a week I am doing a round Ireland trip with 6 people, all their gear and 110 gallons on board. This will considerably increase the weight of the boat and the load on the propeller. My concern is burning out the bushing in the prop with all this extra weight if the conditions are rough.
For this reason I contacted Solas Propellers in the UK. They advise me to fit one of their 4 bladed aluminium props 14" x 21". They figured that I should gain about 300rpm.
After testing the prop last week I actually droped 100 rpm and 7 knots of speed. I sent the prop back and they resupplied me with another 4 blade Aluminium propeller 14.25" x 19" which I obviously thought would be an improvement!
I tested the prop last night and I'm still down 100 rpm (5000rpm max) and I'm actually down a total of 10 knots with the boat only doing 37 knots. I also have lost a lot of acceleration compared to my original 22" propeller!
If anyone can give me their views on this it would be very much appreciated as I only have a week to get the problem sorted.

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Joe

Alan Priddy · 25 July 2001, 10:16

Hi. If you are running heavy loads over long distances the performance figures you have indicated show that you are about right. If you are still running the origanal Alloy prop, upgrade to the same size Stainless.
On a different note,Are you taking part in teh Donagadee RIB raid / Irish sea challange or are you doing soemting by yourself? Spirit will be in N Irleland for a week contact me if you want to meet up for a drink
Alan

tsunami · 25 July 2001, 15:51

Hi Alan,
The prop I'm running on at present is actually stainless steel which is probably why the performance is so good. I had hoped to get a alloy prop as a cheap spare, but would still like to have reasonable performance from it. I'm now trying a 3 blade 14.8" x 19" so hopefully it will return better performance figures.
The trip I'm doing round Ireland is actually just one myself and a few mates involved in the Rib scene thought up a few months ago. Just trying to make all the last minute arrangements now.
I'm not taking part in any organised events this year but hopefully will have a bit more time off to take part next year!
Good Luck with all your ventures in the future.

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Joe

Powerboat · 25 July 2001, 23:29

Just for info , there are a few round Ireland record attempts over the next few days ...one out of Courtmacsherry and one out of Kinsale.

Best wishes ,

Stuart www.powerboat.org

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www.powerboat.org

eksrae · 26 July 2001, 02:51

try raising your motor up one bolt hole this will give you the needed rpm. we run our boat with the prop level with the boat bottom and everything works fine and the boat handles better

tsunami · 26 July 2001, 09:08

Hi Stuart,
I heard that the lads that went in the 6.5m Osprey took an awful hammering up the west coast with one of the crew having to leave the boat in Donegal. I think they arrived in Red Bay sometime yesterday morning.
I'm taking the easy option and going round as a holiday. Taking six days to go to Red Bay in Antrim (my home port) and then possibly one day to come down the east coast back to Kinsale.
We're planning to stay in Cape Clear, Dingle, Aran Islands, Achill Island, Donegal, Tory Island, then into Red Bay so should be a bit off fun.
More boats welcome to come along if they wish??

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Joe

tsunami · 26 July 2001, 09:11

Eskrae,
I might actually try that. I run with the cavitation plate of the engine level with the bottom of the boat. I suppose I could get away with raising it one bolt and see what happens.
Cheers

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Joe