Reply
 
Thread Tools Search this Thread
 
Old 30 August 2010, 13:51   #1
Member
 
Country: UK - England
Town: kingsbridge
Boat name: felix
Make: cesar
Length: 3m +
Engine: yam 20hp
Join Date: Aug 2010
Posts: 31
ceasar mini cat 20hp 2stroke yam prop help

hi iv got a 3.2 mini cat with a yam 20hp on the back

std prop is a 9 7/8 x 10.5 pitch

2 up w.o.t = 27 mph @ 6100 rpm using a tiny tach and gps in flat water

engine is sat about 50mm off the 2" box section as its meant to be so clamps bite on the box i did try it lower no differance

its trimmed out on the second hole out? cant trim out any more as i get loads of prop slip on hole shot and cornering.

steel developments recomender a 13p solas thinned edges bit of extra cup and a progressive pitch from 12 to 13

any advice welcome
__________________

__________________
supremesoundz is offline   Reply With Quote
Old 30 August 2010, 14:52   #2
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
can't really offer any advice but if you decide to get rid of the current prop send me a PM/email with some photos and the price you want for it...
__________________
Poly is offline   Reply With Quote
Old 31 August 2010, 16:21   #3
Member
 
Country: UK - England
Town: kingsbridge
Boat name: felix
Make: cesar
Length: 3m +
Engine: yam 20hp
Join Date: Aug 2010
Posts: 31
it s only a std ally yam prop ?
__________________
supremesoundz is offline   Reply With Quote
Old 31 August 2010, 17:01   #4
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
Quote:
Originally Posted by supremesoundz View Post
it s only a std ally yam prop ?
Aye I know, its the right prop for my engine / boat, and I've got a couple of slightly bent ones sitting here. If you don't need it / its gathering dust / your chucking it out then I'd be happy to give you some beer vouchers for it. But if it would be useful as a spare then hang on to it and I'll send these two off for repair when the bad weather comes.
__________________
Poly is offline   Reply With Quote
Old 01 September 2010, 15:56   #5
Member
 
Country: UK - England
Town: kingsbridge
Boat name: felix
Make: cesar
Length: 3m +
Engine: yam 20hp
Join Date: Aug 2010
Posts: 31
i have just got a solas cupped stainless prop same as std pitch im going to give it a try but im thinking il need a bigger pitch as ive been recomended a 12 cupped if ur interested in it if its no good on mine
__________________
supremesoundz is offline   Reply With Quote
Old 01 September 2010, 21:05   #6
Member
 
Country: Australia
Town: Cairns
Boat name: KAHUNAS
Make: Zodiac
Length: under 3m
Engine: 30 Tohatsu
MMSI: wft is a dsc mmsi ?
Join Date: Jun 2010
Posts: 82
What are you trying to achieve from a prop change? I've got a bit of exp with mini t-cats, but never with a motor as small as a 20, particulary a 4 stroke.

At WOT, your spinning at 6100 rpm, which is just about ideal i'd say, what is the WOT range for a 4 stroke 20 yammy?

Your talking about prop slip, well your going to get that with your motor trimmed out regarless or prop choice. Trimming your motor out sacrifices hole shot, and cornering, for top end speed.

With less prop in the water, you get less drag, more speed in a straight line, but the prop has less bite when cornering. If your trimmed out and want to corner, you will need to sit the bow right up and then corner, otherwise with the bow down, it will just keep slipping, and if you keep and eye on the cav plate, you'll probably see it sits up above water line when your getting prop slip.



With an SS prop, you might get a small gain, bit i'd be inclined to think that the gains of an SS prop, would be more towards having motor fully trimmed out, and your only running 2 out of 3 blades in the water.
__________________
Bus_Boy is offline   Reply With Quote
Old 02 September 2010, 05:56   #7
Member
 
Country: UK - England
Town: kingsbridge
Boat name: felix
Make: cesar
Length: 3m +
Engine: yam 20hp
Join Date: Aug 2010
Posts: 31
hi thanks 4 the reply its a 2 stroke yam auto lube? yh it revs at 6100 2 up 6595 solo?
the wot rev range 4 the yam is 5500 so i was told by yamaha

what size engine have u had experience with? i thought mine was big as the mini cat is rated 4 a 18hp

my top speed is pretty low @ 26 mph ive seen on another forum tht one with a 18hp was doing 56kmph and one with a 30hp doing 76kmph
__________________
supremesoundz is offline   Reply With Quote
Old 03 September 2010, 01:11   #8
Member
 
Country: Australia
Town: Cairns
Boat name: KAHUNAS
Make: Zodiac
Length: under 3m
Engine: 30 Tohatsu
MMSI: wft is a dsc mmsi ?
Join Date: Jun 2010
Posts: 82
These days they rate the mini's to 18hp, previously they were rated to 25hp. 18hp is a very conservative rating for a boat commonly seen with a 30hp.

The 2 i have driven were powered by a 3 cyl 30 Yamaha, and a 2 cyl 40 Tohatsu.

If your talking top speed, then you have to sacrifice on everything else. You need to run as much trim as possible, and also look at raising the motor further up off the transom. It will take forever to plane and get going, and will prop slip and cavitate like crazy until you finally get the hull in a position that allow's minuimum drag, and just enough prop in the water (usually 2 out of 3 blades) which is where an SS prop also comes of an advantage, as they don't flex like a standard prop.

If your bored and got time, check out the likes of Youtube ect, at some video's of T-cats doing speed trials, and it will give you a bit of an indication, just listen to everytime the prop hub (exhaust) comes up above water level.



Ceasor rate the mini with a 18hp to reach speeds estimated at around 35 mph, which is about 56 km/h.

So before you go spending a small fortune on a new prop without any guarantee that it will bring any improvments, i'd suggest doing as much testing as you can with your current setup.

Also on a sidenote, if you want a bit more top end, have a flick through your Yammie's part list, and compare the parts list against the 25 hp model.

20 and 25 are the same cu in dissplacement, and without saying exactly which parts are different (haven't owned a Yammie in a long time) i can almost say for certain that upgrading your motor as per factorty specs to a 25 hp will offer you greater value for money vs new prop.
__________________
Bus_Boy is offline   Reply With Quote
Old 03 September 2010, 03:00   #9
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
Quote:
Originally Posted by Bus_Boy View Post
Also on a sidenote, if you want a bit more top end, have a flick through your Yammie's part list, and compare the parts list against the 25 hp model.

20 and 25 are the same cu in dissplacement, and without saying exactly which parts are different (haven't owned a Yammie in a long time) i can almost say for certain that upgrading your motor as per factorty specs to a 25 hp will offer you greater value for money vs new prop.
It sounds to me like you are using the same engine as me. My 20HP shares the same block as a 25HP 2 pot. The physical differences are: new carbs x 2, and new exhaust manifold. There may be changes to timing etc too - but those are the parts changes. Obviously to get the best out that extra power you would still need a new prop anyway.
__________________
Poly is offline   Reply With Quote
Old 03 September 2010, 05:12   #10
Member
 
Country: UK - England
Town: kingsbridge
Boat name: felix
Make: cesar
Length: 3m +
Engine: yam 20hp
Join Date: Aug 2010
Posts: 31
ideal bus boy i have had a bit of an experiment with the engine height as when i got it it was jacked up so the clamps sat on the box section so i lowered it didnt really change much lost a bit of top end which from what u sed is right and allowed me to trim out one more notch, but after some playing i found it better to be raised on the transom and trimmed in one notch? ive got a like 4 like st/st prop on its wat which a mate has so il try tht b4 forking out?

so i could just change some parts for other oem parts then? i know on the engines we use in ocr that the 115 is the same as the 130 just bigger carbs different exhaust tube timing and power plate?

so like pol just said the carbs and exhaust manifold are the only different part no's and probablt the timing adjusted would be a instant 5hp gain over stock
__________________

__________________
supremesoundz is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 06:05.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.