Got my new rib wet!

[Simon666]

Finally took the new zodiac pro open 550 down to Burnham at the weekend.
Did some playing
Gps showed 45.3 Mph max on flat water after playing with the trim with the standard ally prop (17p) on the Johnson 90 2 stroke @ 5500 Rpm
Does that sound good for the boat? Would a 19" pitch stainless prop make much differance?
It certainly felt fast enough!
I might upload some piccys if i get a min.
Simon

[ADS]

45.3MPH ( 39.3 knots) sounds fast to me, that is probably hull speed on a 5.5m? I am not sure that you will get it to go any faster than that.
What is the rpm range advised by Johnson and whereabouts is 5500RPM within that? Johnson will prescribe a powerband where that 90HP is produced probably 4800-5600rpm at a guess, you want to be propped to be within that range otherwise you won't be getting your 90HP.
I would guess that 5500 is towards the top of the range therefore you could go up in pitch to reduce that a little and you may gain more top end. I believe you lose 250rpm each pitch you go up.
Has it run in yet?

Checkout www.steeldevelopments.co.uk
or phone them and speak to Julie.

Have fun with your new toy

Alex

[Kernow Buoy]

Hi Simon
Congratulations! the only problem you'll have now is trying to get that grin off your face!
I've a similar size Rib with a 90 and also had an alloy 17" which I replaced with a 19" Stainless. Yes it improved top-end by 3kts but also lowered wot by 300/400 rpm The most noticeable improvement was in the lack of ventilation in the turns and hence faster turning, coupled with the ability to trim up more I'd say yes do it.
Have fun
Kernow

[codprawn]

Originally Posted by ADS

45.3MPH ( 39.3 knots) sounds fast to me, that is probably hull speed on a 5.5m? I am not sure that you will get it to go any faster than that.
What is the rpm range advised by Johnson and whereabouts is 5500RPM within that? Johnson will prescribe a powerband where that 90HP is produced probably 4800-5600rpm at a guess, you want to be propped to be within that range otherwise you won't be getting your 90HP.
I would guess that 5500 is towards the top of the range therefore you could go up in pitch to reduce that a little and you may gain more top end. I believe you lose 250rpm each pitch you go up.
Has it run in yet?

Checkout www.steeldevelopments.co.uk
or phone them and speak to Julie.

Have fun with your new toy

Alex

Hull speed? Thought that only applied to displacement hulls - with a planing hull more power = more speed!!!

[Cookee]

Originally Posted by codprawn

Hull speed? Thought that only applied to displacement hulls - with a planing hull more power = more speed!!!

Just as anything - more power = more speed, however Julie is quite right IMHO - planing hulls do have a speed at which it needs a lot more hp to get any faster.

[ADS]

Originally Posted by codprawn

Hull speed? Thought that only applied to displacement hulls - with a planing hull more power = more speed!!!

Applies to planing hulls to Cod, as Cookee says its the point at which small increase in HP make no difference to the top end.
When your boat is finished and you insure it, they will ask you for the maximum design speed.

Alex