Classic SeaCraft Community  

Go Back   Classic SeaCraft Community > General Discussion > Performance

Notices

View Poll Results: Would you stay longer than Fri-Sun??
Yes 6 27.27%
No 16 72.73%
Voters: 22. You may not vote on this poll

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 07-13-2008, 10:52 PM
joehat70 joehat70 is offline
Junior Member
 
Join Date: Jun 2006
Location: long iseland
Posts: 8
Default 23 septre i.o.prop size info

bought 73 septre i.o.with 350-260 hp engine swinging a15.17 alum prop .with 280 volvo drive engine only turns 3850 rpm any body with simaler set up please help.need more rpm.
Reply With Quote
  #2  
Old 07-14-2008, 10:30 AM
1bayouboy 1bayouboy is offline
Senior Member
 
Join Date: Jul 2006
Location: Mount Pleasant, SC
Posts: 592
Default Re: 23 septre i.o.prop size info

Is that puppy running on all 8??? I'm not sure what the WOT range is on that engine, but if I had to guess I'd say
4400-4800 so 3850 is really low. I would also thing a 17 pitch prop would be close to correct for that boat. I have a heavier boat with a 300HP mercruiser turning a 15 pitch Rev 4 up to 5150RPMs. It's a great prop to keep you on plane at lower speed.
Reply With Quote
  #3  
Old 07-14-2008, 11:10 PM
BigLew BigLew is offline
Senior Member
 
Join Date: Jan 2007
Location: Newburyport Area; Massachusetts
Posts: 1,364
Default Re: 23 septre i.o.prop size info

IT is funny this topic should come up. If I've got the same question and the same configuration. I've held off a asking the question because I plan to repower soon, and will likely try and put in a 350 CID Vortex putting out 310-325 horsepower.

One thing not mentioned previously is that some of these boats have tanks holding as much as 145 gallons (mine for example). That is nearly 900 pounds of fuel. Also, in my case, the aluminum prop is cupped. However, I believe mine has reached 4000-4100 RPM. The above mentioned target WOT RPM range is accurate though.

As I said, I will be a REAL interested in the results of this.
__________________
Getting home is more important than getting there!

Plan accordingly!
Reply With Quote
  #4  
Old 07-15-2008, 08:21 AM
BigLew BigLew is offline
Senior Member
 
Join Date: Jan 2007
Location: Newburyport Area; Massachusetts
Posts: 1,364
Default Re: 23 septre i.o.prop size info

Fr. Frank,

Where are you when we need you? Please bless us with your encyclopedic knowledge of all things having to do with marine power.

Bless you brother!
__________________
Getting home is more important than getting there!

Plan accordingly!
Reply With Quote
  #5  
Old 07-15-2008, 04:41 PM
1bayouboy 1bayouboy is offline
Senior Member
 
Join Date: Jul 2006
Location: Mount Pleasant, SC
Posts: 592
Default Re: 23 septre i.o.prop size info

My sentiments exactly of Fr Frank....

I can tell you his usual is max should be max at max....

Meaning your max rpm should hit the max end of the range when you boat is max loaded out. I propped mine accordingly and could over rev it when lightly loaded if I tried or come very close. The max rpm on the 350MAG Horizon is an insane 5200rpms. The only time I come close is a brief WOT run every other time out.
Reply With Quote
  #6  
Old 07-16-2008, 08:20 AM
Fr. Frank Fr. Frank is offline
Senior Member
 
Join Date: Oct 2003
Location: Shalimar, Florida
Posts: 2,265
Default Re: 23 septre i.o.prop size info

Two possibilities: Either the motor is not developing full power, or you need a different prop. First make sure your motor is running well.

As to your prop, I can't get you close without knowing your gear ratio. According to my book, the Volvo 280 series single prop outdrive was available with six different gear ratios over the years, 1.5:1, 1.61:1. 1.65:1, 1.73:1, 1.88:1 and 2.08:1.

Here's the formula:

. SPEED X RATIO X C
PITCH = ( -------------------------- )
. RPM X [1 - (SLIP/100)]

If we assume the speed is 36 statute miles per hour, the C in the above equation is equal to 1056. We will also assume an average propeller slip of 15%, and a max RPM of 4800. Now the equation looks like this:

. 36 X RATIO X 1056
PITCH = ( -------------------------- )
. 4800 X [1 - (15/100)]

So give me your drive ratio, and assuming a clean hull bottom, I'll give you a style, diameter and pitch prop to put you in the sweet spot for rpms. Deal?

Of course, knowing the present pitch, speed, rpm, and using 15 as an approximate slip ratio can give you a pretty close estimate on your gear ratio if you can't find it anywhere else.

. RPM X PITCH X [ 1 - (SLIP/100) ]
RATIO = ( ---------------------------------- )
. SPEED x C
__________________
Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.

Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!

Currently without a SeaCraft
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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

Forum Jump


All times are GMT -4. The time now is 02:55 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
All original content © 2003-2013 ClassicSeacraft