Trojan Boat Forum

I have not been able to help but wonder for the past year and a half why the F – 36 powered with Chrysler 440s at a total of 660 hp is propped the same as one that is powered by 454s totaling 700 hp. Curious about going four blade and with something that will give a bit more speed at cruise. I am also wondering, for those of you with 454s and the factory 20 x 21 props, what have you been able to achieve for max RPM at WOT.

The 454 are slightly more HP but it is at a higher rpm .


I may add many are running 20x20

I have a 36' Tri Fly with twin 400s and it's rocking these 4 blade 20" props
I don't know if they are original or not, I suspect they are, as the rest of the boat has been poorly maintained and I doubt the PO did anything to it, let alone change out the props

I have an f36 tri-cabin with twin 270s, having not as yet had the boat on the hard to look, does anyone know what props I would expect to find there?

I have a F36 Sportfish. She has 330HP GM 454s spinning 20x20 3 blade props (at least that is what they are marked). Back in 2010, I had just installed fuel flow meters and posted this data:
RPM /MPG /MPH /Port GPH /Starb GPH /Total GPH
750 /1.63 /4.74 /1.3 /1.6 /2.9
1000 /1.69 /5.75 /1.4 /2 /3.4
1250 /1.44 /7.78 /2.6 /2.8 /5.4
1500 /1.36 /8.7 /3.4 /3 /6.4
1750 /1.18 /10 /4.9 /3.6 /8.5
2000 /1.13 /10.8 /5.1 /4.5 /9.6
2250 /0.95 /11.3 /6.9 /5 /11.9
2500 /0.74 /12.8 /9.2 /8 /17.2
2750 /0.88 /17.6 /10 /10 /20
3000 /0.74 /21.3 /16 /12.9 /28.9
3250 /0.75 /26.5 /18.5 /17 /35.5
3500 /0.75 /30 /18.6 /21.4 /40

About once a month, I'll run at WOT on the way back to our marina from a pump out, which is about 3800 RPM, but it won't go past that which means I must be a little over-propped (or I need to get some crap unloaded from the boat). Also, I really don't see GPS speed change much after 3500 RPM so I'm assuming I'm just losing the extra RPMs to slip. The longest I run at 3000 RPMs is about 1.5 hrs as 30 miles is about all the open water there is between locks on the MIssissippi, sometimes less. You might also note that my starboard engine drinks a little more fuel than the port. I've tried to figure that out a few times, and finally chalked it up to error in the cheap Lowrance fuel flow gauges I have installed.

IMHO, these boats are not built for speed... or I can afford to run it like a speed boat. I'd say, 90% of the time, I run below 2000 RPM and half of that is around 1200. On my budget, I can go on a 300 mi trip down and back up he river and burn 200 Gals @ $4 gal = $800 and take a week or I can burn up $1600 on the same trip in 2 days.

Not sure if this is what you are looking for, but perhaps it will help with your puzzle.

LandVF36 wrote:You might also note that my starboard engine drinks a little more fuel than the port. I've tried to figure that out a few times, and finally chalked it up to error in the cheap Lowrance fuel flow gauges I have installed.

The fuel flow gauges are probably telling you the truth. With my Chrysler 360s, one of my tanks consistently takes about 10% more at fill-ups than the other.

You would think, but when I make long trips, and have the values on the gas lines right, she burns pretty much evenly between sides. I did have a problem with the cross-over gas line valve at one time, and I was burning almost all the fuel from one side, but when its closed right, its pretty even burn on a trip as long as I don't run the genny much..

Ive noticed the same thing ....pulling more from one side so i closed the crossover valve too

liquids, gasses, and electricity will always take the path of least resistance...

Barrie, when you're running at 3000 RPMs, how many knots are you going and are those 20 x 20 or 20 x 21?

Duchessofmilford wrote:Barrie, when you're running at 3000 RPMs, how many knots are you going and are those 20 x 20 or 20 x 21?

Sorry, I don't know any of that.
I've never had the boat out, it's a project for now
I can check the prop info though.