Trojan Boat Forum

This response is addressing your first project, reproping your boat.

If you are considering having your boat analyzed by a computer you will need to provide the information necessary for the program. The analysis will only be as accurate as the information entered. You will need a log of data of speed at specific RPM ranging from 1000 RPM to WOT in increments of 100 RPM in different sea conditions, wind, and currents. You should know what the boat is doing in head, beam, and following seas. How clean the bottom is is also important. The drag of a dirty bottom can significantly slow a boat.

If you don’t have the data you will want to fix your throttle cable and get as much data as you can before you pull the boat.

That being said, your props are the gearing of the engine. The perfect props for a boat will transfer the maximum power of the engine to the water giving the maximum thrust and limit the engines WOT RPM to the manufactures limit. I believe the Chrysler 318 has a maximum of 4400 RPM. Most likely you won’t be able to reach that rpm. Most likely our boats are heavier then when they were built. We have added many personal items, plus the boat has absorbed water making it heavier.

gjrylands wrote: plus the boat has absorbed water making it heavier.

Only thing I disagree with... solid glass hull should not absorb water. If one's cored decks are that wet to add much weight then they should be fixed.

You have not said what dia and pitch your props are. My guess if the 13 is pitch is that it is way too low for that boat.

On my F32 I use 17x14 4 blade or 16x15 3 blade with twin 318's.
Your boat is smaller and lighter so I would expect your pitch could be higher than the 13.
Have you called John at Marine Tech to ask him what they should be? Fax: 717-684-8331

You said you were turning 13" props. What is the pitch? If you are over propped, it will overload the engines and alter the power curve.

I had a '69 31' Trojan with 318s. It weighed 8000 lbs. It ran much faster then what you are reporting. The boat had 14x11 props from the factory. After adding a bridge and glassing the hard top I changed to 14x10 with a cup. I was able to cruse at 17kts at 3000 rpm. When I opened it up, which wasn't very often, it ran between 26 and 27kts. At that speed it was a bit too unstable.

ready123 wrote:You have not said what dia and pitch your props are. My guess if the 13 is pitch is that it is way too low for that boat.

On my F32 I use 17x14 4 blade or 16x15 3 blade with twin 318's.
Your boat is smaller and lighter so I would expect your pitch could be higher than the 13.
Have you called John at Marine Tech to ask him what they should be? Fax: 717-684-8331

You have a gear reduction in the trans. I think you have a 1.5:1 vetvet drive. The F30 has a 1:1 velvet drive.

ready123 wrote:

gjrylands wrote: plus the boat has absorbed water making it heavier.

Only thing I disagree with... solid glass hull should not absorb water. If one's cored decks are that wet to add much weight then they should be fixed.

Bull ,not like wood but they will absorb some , thats why they make barrier coatings . glass absorbs water and if there is voids you get blisters

http://books.google.com/books?id=RUjh0N ... q=&f=false

prowlersfish wrote:

ready123 wrote:

gjrylands wrote: plus the boat has absorbed water making it heavier.

Only thing I disagree with... solid glass hull should not absorb water. If one's cored decks are that wet to add much weight then they should be fixed.

Bull ,not like wood but they will absorb some , thats why they make barrier coatings . glass absorbs water and if there is voids you get blisters

http://books.google.com/books?id=RUjh0N ... q=&f=false

You bet! Fiberglass is pourous.... so is gelcoat. Gelcoat is just not as pourous.

Mike, if you need new props, check with Ellis propeller in Jacksonville Florida. The made a new nibral 13" 3 blade prop for me for $390. Hollar at me if you'd like the number.