1979 Tolly 30 Prop Size

[Phil Dyer]

Hi, I'm restoring a 1979 Tolly 30 and was stretched to a 34 and has Chevy 350 twin engines.  The boat is a TOTAL restoration.   I'm trying to figure out the proper prop size it should have.   The shaft is 1 1/4" and the transmission gear ratio is 1-1.5.  Any idea what the prop size should be?

[Brian Edmondson]

HI Phil,

I am NOT an expert and that's what you need to address the prop question.  There is a fair amount of info out there on prop sizing, but there's a lot of science to it and - particularly because of the 4' stretch - your boat is unique.  For example, there are a LOT of Tolly 34s out there, but your boat is way different from them... so you can't just do what they are doing.  FYI - I am heading into four years in my restoration of a 1983 Tolly 26 Sedan.  It's been BRUTAL, but also a labor of love and I am still enjoying both the work and the challenges as I turn 67 today.  I have hundreds of pictures, some of which have been uploaded to the Tolly group.  More would be there but I want to concentrate on getting my boat back in the water. 

Just a couple of quick and amateurish (initial thoughts/opinions) that may be of value to you:

• My 26 has a single Chevy 350.  I have not run it on the water yet... hopefully soon... but on the dyno that engine is amazing.  The HP is close to the original Crusader 270 at 274hp, but the torque is 385 ft lbs and it peaks early... at only 2,400rpm.  I built this engine to many of the specs and recommendations from Dennis Moore, so I call this "A Dennis Moore Engine." 
  
• The only thing I see beating diesel, is electric power, and I think we are about 10 years away from that.  I hope to pull my SBC and gas tanks and go to full electric power before I hand Symphony off to my sons and grandson.  I might be dreaming here.
• My single screw shaft size is 1.25" like yours.  My 19x20 (OEM) prop is 1" behind the strut and the blades spin withing 1" of the hull.  All of this is original Tolly equipment/spec.  The 1983 Chevy 350 with three bad cylinders would push the boat to 27mph.  The compression on those three bad cylinders was 90, 54, 50psi.  The piston skirts were broken off of two of the bad pistons.  I've got pics of all of this.  But my point here is, if we're talking gasoline, the SBC is the best.  I would even take it over the big blocks.  I expect to run well above 30mph and will hopefully find a sweet spot where I get the best economy possible out of a gasoline engine... unless we're talking about staying at "hull speed" at 7mph.  That's a different discussion.
  
• Diesel:  I thought about this a LOT and chose to stick with gasoline (which I kinda hate) as my Tolly 26 (I don't think) will ever be that valuable of a boat.  If money is not a primary consideration, nothing beats diesel from both a fuel economy and (more importantly) a safety perspective.  BUT, low-dollar-value might NOT be as significant for your 34.  When I am done, I will have $60k in my boat counting a pretty sweet brand new 3-axle trailer; and I think I would be lucky to find somebody who will give me $30k.  Converting to diesel, in my opinion, is a fairly serious engineering project.  It is SO easy to get it wrong and I've seen it happen.  First of all, you don't just need new engines, you need new everything... especially transmissions.

Good luck with this... but more important than luck... I think... is homework.

Brian Edmondson

Kent, WA

[bill]

I have change props on two boats, and had a good experience with Jim Thelan at  Acme Prop.  They have a formula that seems to work for any boat,
and can be fine-tuned.  The props are CNC'd, and our local prop shop says they are the best the've ever seen. Try jth...@acmemarine.com - you have to be persistent,
he seems like he has a lot going on.

On Tuesday, November 17, 2020 at 10:36:28 AM UTC-8 phildy...@gmail.com wrote: