Avon SR4 Project

[Chris Caton]

Originally Posted by HUMBER P4VWL

Sweet Chris. Perfect for you ......as I guess as opposed to the revenger you can lift her back to the waters edge when you take too long over a pint and the tide goes out! ;-)

sad thing is Paul, I didnt even have the extra pint, I was on coffee but, the SR4 is brill, you should get yourself one, be just the ticket for a evening cruise up the dee with the young'uns

[HUMBER P4VWL]

Yes I know. With what we've spent on the tubes recently we could have had one too!! :-(

[Chris Caton]

maiden voyage, went well but needs a bigger prop, hitting the rev limiter with a 11" dia. x 13" pitch

[Chris Caton]

11" dia. x 14" pitch a bit better, but needs at least a 15" pitch to get the performance up

[Nick Hearne]

Sweet. How is she, dose she feel stern heavy? As she looks well balanced!
Looking very smart

[Chris Caton]

feels just right Nick, not sure if it's a bit stern heavy but as it's the only SR4 I've been on nothing to compare with, but still goes well with two on board and undersized prop, hopefully when right prop fitted it will go better again, more than happy so far, great fun

[Barrowboy]

Originally Posted by Nick Hearne

Sweet. How is she, dose she feel stern heavy? As she looks well balanced!
Looking very smart

Stern heavy?

She looks well balanced because she is!

(for those of you who haven't had the pleasure of meeting Mr C, eeez a big la'!)

[Anchorhandler]

Looks great Chris... They are good fun aren't they?? ;-)

I was surprised how well mine handled the choppy stuff... We did a 53 mile trip in ours last month some of it less than favourable conditions and, apart from the wind blowing the bow spray back at us, the whole trip was done pretty comfortably. the little SR4 definately punches above its weight.

Out of curiosity, what prop are you currently running? I'll need to check but I think I've got a 12p fitted. it'd be interesting to see the difference in performance between our two sister ships!!

Simon

Sent from my Experia Ultra europallet using Rib.net

[Nick Hearne]

Originally Posted by Barrowboy

Stern heavy?

She looks well balanced because she is!

(for those of you who haven't had the pleasure of meeting Mr C, eeez a big la'!)

Are you saying it is balanced because Chris is large?

If so then this would explain why my Sr4 with a 50hp 2st with me and family in is rather tail heavy as I'm a light weight!

[Chris Caton]

Originally Posted by Barrowboy

Stern heavy?

She looks well balanced because she is!

(for those of you who haven't had the pleasure of meeting Mr C, eeez a big la'!)

I prefer "stocky" Tony

Originally Posted by Anchorhandler

Looks great Chris... They are good fun aren't they?? ;-)

I was surprised how well mine handled the choppy stuff... We did a 53 mile trip in ours last month some of it less than favourable conditions and, apart from the wind blowing the bow spray back at us, the whole trip was done pretty comfortably. the little SR4 definately punches above its weight.

Out of curiosity, what prop are you currently running? I'll need to check but I think I've got a 12p fitted. it'd be interesting to see the difference in performance between our two sister ships!!

Simon

Sent from my Experia Ultra europallet using Rib.net

excellent fun Simon, even on a run from Caernarfon thru the Swellies to Puffin Island not a drop of spray, which included some enthusiastic driving

started off with a 11" dia. X 13" pitch which induced revving out at around 30mph, currently running a 11" dia. X 14" which is now giving around 35mph, but still hitting 6200rpm, hopefully got a 11" dia. X 15" pitch on the way to try next time, but maybe need to go even bigger, I'd like to get up to around 40mph but reduce the revs to around 5500 to 5750'ish, but it's all a guessing game!

Originally Posted by Nick Hearne

Are you saying it is balanced because Chris is large?

If so then this would explain why my Sr4 with a 50hp 2st with me and family in is rather tail heavy as I'm a light weight!

it didn't seem to make much difference if I was on my own or when Jayne was on the back seat, there again Jayne is just a touch lighter than me, just

[keg]

It looks like you had a great time Chris.

I'm a shade over 12st...... quite a big shadow actually and my SR4 seems well balanced.

I only have a single seat console and i have no idea what size or pitch the prop is.

As a relative newbie, how can i tell size and pitch please? is it stamped or engraved somewhere?

[Nick Hearne]

They I say my SR4 is tail heavy this is down to load/people in the boat wanting to sit at the back, it is fine when well loaded or just me!

Marking should be stamped on the prop!

[Chris Caton]

Originally Posted by keg

It looks like you had a great time Chris.

I'm a shade over 12st...... quite a big shadow actually and my SR4 seems well balanced.

I only have a single seat console and i have no idea what size or pitch the prop is.

As a relative newbie, how can i tell size and pitch please? is it stamped or engraved somewhere?

I'm a shade over 12st myself, just

as Nick says, prop size should be stamped on the prop, or you may find it by taking the split pin, nut and washer off and looking on the end of the splined hub

Originally Posted by Nick Hearne

They I say my SR4 is tail heavy this is down to load/people in the boat wanting to sit at the back, it is fine when well loaded or just me!

Marking should be stamped on the prop!

is that a 11.75 x 17" prop you're using on your SR4 Nick?

[Nick Hearne]

Originally Posted by Chris Caton

is that a 11.75 x 17" prop you're using on your SR4 Nick?

I do still use this one (it is on it at the moment) but it is way over propped and will only hit 4100rpm, I bought from steel developments a aluminum 11.3 X 13 on there recommendation which is spot on and will hit max rpm now and even managing to pull me skiing
Top end speed is about the same.

[Chris Caton]

Originally Posted by Nick Hearne

I do still use this one (it is on it at the moment) but it is way over propped and will only hit 4100rpm, I bought from steel developments a aluminum 11.3 X 13 on there recommendation which is spot on and will hit max rpm now and even managing to pull me skiing
Top end speed is about the same.

I tried a 11 x 13 and it was hitting the rev limiter but only giving me around 30mph, it's definitely black magic this prop lark

[palsteg]

Originally Posted by Chris Caton

started off with a 11" dia. X 13" pitch which induced revving out at around 30mph, currently running a 11" dia. X 14" which is now giving around 35mph, but still hitting 6200rpm, hopefully got a 11" dia. X 15" pitch on the way to try next time, but maybe need to go even bigger, I'd like to get up to around 40mph but reduce the revs to around 5500 to 5750'ish, but it's all a guessing game!

Hi Chris,

my congratulations to that one, really niiice!

RPM and speed should´nt only be a "guessing game", no black magic!

You know your gear ratio 2,08, you know the pitch of the prop, you know the rpm, and you know the slippage of the prop on that boat type
approx 10 %

You say 6200 rpm / approx 35 mph / 14 pitch

Let me calculate in centimetres, metres and kilometres per hour, it´s easyer for a german one.
35 mph ( x 1,6) = 56 kilometres per hour

One turn around of a 14 pitch prop (x 2,54 cm) = 35,56 cm forwards (1 inch = 2,54 cm)
minus 10% approx prop slippage = 32 cm forwards

6200 rpm : 2,08 gear ratio = 2980,77 prop turn arounds per minute
2980,77 x 32 cm forwards = 95384, 62 cm
95384,62 cm : 100 = 953,85 meters per minute
953,85 metres x 60 minutes = 57231 metres per hour
57231 metres per hour : 1000 metres = 57,23 kilometres per hour
57,23 kilometres per hour : 1,6 = 35,76 mph

perfect match to your data, no magic, no guessing.

You can calculate it out, not yust a guessing game.

Your plan is 40 mph with approx 5625 rpm. What pitch you need?
I would say 17 pitch. Lets calculate......

17 pitch x 2,54 cm = 43,18 cm, minus 10% slippage = 38,86 cm
(one prop turn around)
5625 rpm : 2,08 gear ratio = 2704,33 prop turn arounds per minute
2704,33 prop turn arounds x 38,86 cm = 105090,26 cm per minute
105090,26 cm : 100 = 1050,90 metres per minute
1050,90 metres per minute x 60 = 63054 metres per hour
63054 : 1000 = 63,05 Kilometres per hour
63,05 kilometres per hour : 1,6 = 39,41 mph

does your engine have enough power to match to this theoretic stuff?

I would better go up to 5850 rpm, and take a 16 pitch one, cause with a
17 pitch may be acceleration is lost too much....and anyway,
there is some chine dance waiting on you. Speed isn´t the whole game,
yust check out 15, 16, 17 pitch if you have the chance to do, to figure out comfortable mix of quick ride and E-Nuff acceleration.

Best regards

Heino

[Chris Caton]

Heino, top to you for the maths

I was "guessing" that I may end up with a 15 or 16" prop and that a 17" may give me top end speed but the effort required to get the rib moving would not justify the 17, although I hadn't figured in any chine walking, but your calculations take the guessing out of the game I'm thinking I may end up somewhere between a 15 & 16" ally prop depending on how the SR4 behaves at the speeds generated by the prop, I'm not looking for high top end speed, but more comfortable top speed with good pickup especially when there's two people on board, maybe I'll end up with a 15" prop when were both on board and a 16" when it's just me............

but either way, I'm really enjoying the SR4 so far, it's great fun

[Barrowboy]

Originally Posted by palsteg

Hi Chris,

my congratulations to that one, really niiice!

RPM and speed should´nt only be a "guessing game", no black magic!

You know your gear ratio 2,08, you know the pitch of the prop, you know the rpm, and you know the slippage of the prop on that boat type
approx 10 %

You say 6200 rpm / approx 35 mph / 14 pitch

Let me calculate in centimetres, metres and kilometres per hour, it´s easyer for a german one.
35 mph ( x 1,6) = 56 kilometres per hour

One turn around of a 14 pitch prop (x 2,54 cm) = 35,56 cm forwards (1 inch = 2,54 cm)
minus 10% approx prop slippage = 32 cm forwards

6200 rpm : 2,08 gear ratio = 2980,77 prop turn arounds per minute
2980,77 x 32 cm forwards = 95384, 62 cm
95384,62 cm : 100 = 953,85 meters per minute
953,85 metres x 60 minutes = 57231 metres per hour
57231 metres per hour : 1000 metres = 57,23 kilometres per hour
57,23 kilometres per hour : 1,6 = 35,76 mph

perfect match to your data, no magic, no guessing.

You can calculate it out, not yust a guessing game.

Your plan is 40 mph with approx 5625 rpm. What pitch you need?
I would say 17 pitch. Lets calculate......

17 pitch x 2,54 cm = 43,18 cm, minus 10% slippage = 38,86 cm
(one prop turn around)
5625 rpm : 2,08 gear ratio = 2704,33 prop turn arounds per minute
2704,33 prop turn arounds x 38,86 cm = 105090,26 cm per minute
105090,26 cm : 100 = 1050,90 metres per minute
1050,90 metres per minute x 60 = 63054 metres per hour
63054 : 1000 = 63,05 Kilometres per hour
63,05 kilometres per hour : 1,6 = 39,41 mph

does your engine have enough power to match to this theoretic stuff?

I would better go up to 5850 rpm, and take a 16 pitch one, cause with a
17 pitch may be acceleration is lost too much....and anyway,
there is some chine dance waiting on you. Speed isn´t the whole game,
yust check out 15, 16, 17 pitch if you have the chance to do, to figure out comfortable mix of quick ride and E-Nuff acceleration.

Best regards

Heino

On the face of it that's very impressive, particularly as it seems the figures were calculated in the early morning hours of the morning (probably after a few schnapps to celebrate winning some football tournament, or other) but they're totally flawed I'm afraid.....

You've completely forgotten to factor in the 12 stone of the person at the helm. So where you've factored in a 10% figure for 'slippage', I suggest you rework the figures and include (say 20%) for 'tonnage'.

It was a good try though.

My money's on a 16" by the way.

[palsteg]

Originally Posted by Barrowboy

On the face of it that's very impressive, particularly as it seems the figures were calculated in the early morning hours of the morning (probably after a few schnapps to celebrate winning some football tournament, or other) but they're totally flawed I'm afraid.....

You've completely forgotten to factor in the 12 stone of the person at the helm. So where you've factored in a 10% figure for 'slippage', I suggest you rework the figures and include (say 20%) for 'tonnage'.

It was a good try though.

My money's on a 16" by the way.

I wasn´t drunk, (at that moment!) and it´s not flawed. It´s always approx about the value of propeller slipping, boat type....influenced by many many many many values.
In that Rib range aproxx 10% is a good value taken over the thum.

Please give me your exact Yamaha outboard model, and i´ll figure out the gear ratio, or yust give me your gear ratio. Give me your top speed rpm, your actual prop pitch, and don´t tell me how fast you go, cause i will calculate this with 10% prop slipping value, would this be fine to you?

Let´s see what happens, but please be honest in the end about your "matching" or not matching top speed.

[keg]

I don't weight tons, just a few stones so less of the tonnage and more of the stoneage please!