Reply
 
Thread Tools Search this Thread
 
Old 29 April 2008, 10:49   #1
Member
 
Country: UK - England
Town: solent
Make: morbass
Length: 5m +
Engine: 55hp mariner
Join Date: Mar 2007
Posts: 121
prop size

hi im after advice on prop size for my tohatsu 50hp on a tohatsu 5.5 rib i think it has the standard prop on it all i can see is c13.5

when turning it seems to loose grip and it doesnt like trim much either.

any advice will be much appreciated

andy
__________________

__________________
lucky ribster is offline   Reply With Quote
Old 29 April 2008, 12:05   #2
Member
 
Locozodiac's Avatar
 
Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider Boats
Length: 4m +
Engine: Tohatsu 18 /30 HP
Join Date: Sep 2007
Posts: 1,706
[QUOTE=lucky ribster;246829] hi im after advice on prop size for my tohatsu 50hp on a tohatsu 5.5 rib i think it has the standard prop on it all i can see is c13.5

when turning it seems to loose grip and it doesnt like trim much either.

any advice will be much appreciated

andy [/Q

Full throttle to ( WOT) a tacho will be needed, read your max tacho reading, compare to max rated rpm's for the Toh 50, play with a higher pitch prop to increase rpm if needed and obtain best top end speed but will lower your hole shot power. Should not pass the max rpm rated for that engine. See the manual, there's prop sizes info available to match your engine. Engine heights factory recommended are very important, see if gap is inside therir parameters in order for the boat to perform well.

Happy Boating
__________________

__________________
Locozodiac is offline   Reply With Quote
Old 02 May 2008, 07:28   #3
Member
 
Country: UK - England
Town: solent
Make: morbass
Length: 5m +
Engine: 55hp mariner
Join Date: Mar 2007
Posts: 121
cheers locozodiac

the max rpm range is 5150-5850 .

i think we was pulling 5200 ish at wot with 3 up and lots of fuel.

i would just like a prop with better grip- any ideas ?

andy
__________________
lucky ribster is offline   Reply With Quote
Old 02 May 2008, 10:46   #4
Member
 
Locozodiac's Avatar
 
Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider Boats
Length: 4m +
Engine: Tohatsu 18 /30 HP
Join Date: Sep 2007
Posts: 1,706
Quote:
Originally Posted by lucky ribster View Post
the max rpm range is 5150-5850 .

i think we was pulling 5200 ish at wot with 3 up and lots of fuel.

i would just like a prop with better grip- any ideas ?

andy
Keep in mind that for every pitch number about 200 revs are involved and you need 600 revs higher, theorically 3 numbers off. If you have already a C-13.5 look for at least 2-3 higher pitched props to give you very near or 5850 revs.

Better ask the Toh dealer to suit you with the proper prop, unless you have lots of different prop pitches to test one by one and useless if you do not have a tacho on the engine to see the difference readings on how the rpm goes higher with a higher pitched prop tested, a matter of trail & error water test.

One issue still not clear is: Nobody knows as exact sciense if you should wot your boat/engine configuration with just one mate/few gallons of gas/almost empty or wot as you would usually use it, that is with more ? mates, full gas tank and lots of things inside. In my particular case have prop/wotted my sib/ engine with just me, 2 gallons of gas and an empty sib and at full throttle just 50 rpm less that max engine rpm which is 5800, with 1 higher pitch. When I'm alone, will know that at full throttle my engine will be reving at the limit of the max rpm without problems, with more weight will rev less but still safely between min and max rpm to that engine. That's way engines are being delivered with intermediate props so you can pitch play and adjust for your type of boating needs.

Have taken the nuisance to write several engine manufacturers and ask them the same tech question, no one has ever answered back, so probably they don't lnow for sure neither which is the correct answer. Bottom line, you don't cruise at wot all the time, so to have a little more or less rpm at wot won't do no harm to any engine. Even Ribnetters have dispare positions about both tech issues.

Happy Boating
__________________
Locozodiac is offline   Reply With Quote
Old 02 May 2008, 22:08   #5
Member
 
Country: UK - England
Town: solent
Make: morbass
Length: 5m +
Engine: 55hp mariner
Join Date: Mar 2007
Posts: 121
thank's again locozodiac

before i speak to the local dealer i will try the normal load of 2 up feul/kit and give that a go next time im out.

1 less might give me another 200 rpm (fingers crossed)

andy
__________________
lucky ribster is offline   Reply With Quote
Old 03 May 2008, 11:31   #6
Member
 
Locozodiac's Avatar
 
Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider Boats
Length: 4m +
Engine: Tohatsu 18 /30 HP
Join Date: Sep 2007
Posts: 1,706
Quote:
Originally Posted by lucky ribster View Post
before i speak to the local dealer i will try the normal load of 2 up feul/kit and give that a go next time im out.

1 less might give me another 200 rpm (fingers crossed)

andy
Do a first wot test on calm waters if possible with yourself alone, a second test like before + 1 mate, for sure will have higher revs than before. Checking the manual you need a C14.5 or C16 prop to be near 5,850 revs.

See you have in use a Tohatsu rib with a 50 HP engine. If going to the dealer ask if your hull needs to be inside the Toh parameters 1-3 cm from boat's bottom to anticavitation plate, at least sibs needs to, don't know about ribs. This is to avoid escesive water splashing inside cause of leg issues, this info is inside the Toh 50 owers manual.

Ask also which is best, wot test single/few gas gal/empty boat or as you would usually use it, more mates, more gas, beers, etc. Would like to know his opinion on this important issue. It's being quite common to have more than 1 prop, you could have one intermediate all purpose and a second with different higher pitch for wot cruising ,skiing, etc. Be sure to use a tacho when at trial & wot and don't pass 5,850 revs.

Happy Boating
__________________
Locozodiac is offline   Reply With Quote
Old 03 May 2008, 12:41   #7
Member
 
Country: UK - England
Town: solent
Make: morbass
Length: 5m +
Engine: 55hp mariner
Join Date: Mar 2007
Posts: 121
will do

it does have a tacho fitted so will test as you say.

i wont get out for a couple of weeks but will let you know how i get on

cheers for yor help.

andy
__________________
lucky ribster is offline   Reply With Quote
Old 03 May 2008, 15:32   #8
Member
 
Hightower's Avatar
 
Country: UK - England
Town: Fareham
Length: 6m +
Join Date: Sep 2003
Posts: 7,855
Just a thought! Don't discount engine height at this stage, if you're losing grip it could be that all that's needed is to lower the engine.
__________________

__________________
Andy

Looks Slow but is Fast
Member of the ebay Blue RIB cover club.
Hightower 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 21:28.


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