Trojan Boat Forum

Well I finally was able to get Capt Ross out of his lazy-boy and onto my boat the Plan Sea. As some of you will remember, I've had lots of issues with power verses speed etc. I had both carbs re-built and jets and rods changed, had the bottom scraped and cleaned, and I needed Ross on board just incase the Plan Sea got too fast for me to handle! But alas it was not to be and Ross forgot his magic wand.
1974 F36 w/400 cu in 280hp chryslers 1.91 gears 20x20 props
2500 rpm wot. 18.2 mph with tide
2400 rpm wot. 14.6 mph against tide
Interesterting enough with one engine in neutral either engine would turn 2400 rpm and produce 10.5 mph.
I have checked timing, advance, plugs wires,and even changed my underware, but still cannot get on plane. We had tabs fully down.
Therefore i am ready to concede and begin a search for new props. The calculation from Boat Diesel recomends a 20x16 or 19x15 in prop. I have 1 3/8 shafts. Anybody out there with something close to that size that you would like to unload pls post or PM me. It is still warm here in Charleston. Larry

20x16 or 19x15 ? thats a big difference between the 2 . Btw Have you checked the tachs ? is the bottom clean ?

Using the same calulator I came up with 20x17 or 19x18 No cup . target / rated rpm I used was 4000 rpm . But the Calulator will very on the numbers you put in ,

You could have your props repiched to 20x17 and try it .

I've got my popcorn.....

alexander38 wrote:I've got my popcorn.....

Why ?

alexander38 wrote:I've got my popcorn.....

can you pass the butter please?

Going back in to your history Me and rossjo used sligty difrent numbers ( I used slightly less rpm and more weght ) But our rusults are real close
I was using no cup and rossjo was using cuped , his results were 19x17 or 20x16 cupped , I think the 19x15 was a typo . a 20x17 or a 20x16 cupped should give close to the same ruslts . ask your prop shop what the can do with a 20x20 . I think were on the same page here or real close

sorry guys but put your pop corn away ,

Thanx Paul, I couldn't understand the 19x15 either. The prop shop i talked with didn't really want to take more than 2 in of pitch out of my 20's. I have located a pair of nibral 20x19 four blade props but I don't think there is enough difference there. Something will turn up I'am sure. Don't you think the old "rule of thumb" 200 rpm per 1 in of pitch is pretty accurate? Larry

Just to clear the record, I nor BoatDiesel's Prop Calculator ever said 19x15.

Larry typed 20x16 and 19x15 instead of 20x15 and 19x16 by mistake - probably during the underwear change (I about had to change mine after watching those 400's with WOT 4-barrels sucking down fuel for 15-20 minutes).

It recommended 19x16, Cupped 3-Blade Props for a max of 23.5knots.

IF you insist on repitching a 20" diameter prop, it recommends 20x14.8 Cupped, and does not say if they should be cupped or not.

As for my own opinion, the engines now sound very strong and 20x17 (from 20x20) would raise the RPM about 600 from 2,400 to 3,000 and might make it. That's about where I would start myself (if these props can be found affordably).

Too early for popcorn ... guess I nibble on some bacon ...



For reference, here were the calculations ...

Power Required Calculator _______________________________________

Hull ........................ Slow Planing
Weight ................... 18,000 lbs
Water Line Length ... 34 feet
Engines .................. 2
Transmission .......... Straight Drive
Desired Speed ........ 25 knots cruising

Speed
To Achieve a Cruising Speed of 25 kts
Required Power
Total At Props: 500 SAE hp 373 kW
Total At Flywheels: 515 SAE hp 384 kW
At Flywheel per Engine: 258 SAE hp 192 kW
Select Engines(2):
Rating ...... SAE HP Metric HP kW Max Kts*
Pleasure ..... 368 ...... 373 ... 275 .. 30.3
Light ........... 322 ...... 327 ... 240 .. 28.4
Medium ....... 286 ...... 290 ... 214 .. 26.8
Heavy ......... 263 ...... 267 ... 196 .. 25.6

Prop. Calculator_______________________________________________

Hull ........................ Slow Planing
Weight ................... 18,000 lbs
Water Line Length ... 34 feet
Engines .................. 2
Output ................... 280 SAE HP
Maximum RPM ........ 4,200
Cruising RPM .......... 3,000
Transmission Type .. Straight Drive
... Ratio .................. 1.9 : 1
Propellor ................ 3 blades
... Cupped Blade ..... Yes
... Prop Diameter .... 20 inch

MAX PERFORMANCE
Available Power: 543.2 SAE hp ( 405.1 kW) @ 4200 RPM
Max Speed: 23.5 kts
Fuel: 33 US Gall/Hr (typical)
CRUISING PERFORMANCE
Cruising Power: 219 SAE hp ( 163.3 kW) @ 3000 RPM
Cruising Speed: 14.9 kts
Fuel: 13 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 19.0 in. Pitch: 16.0 in.
Blades: 3 Cupped: Yes
Transmission Ratio Acceptable
PROPELLER BASED ON INPUT DIAMETER
Diameter: 20.0
Pitch: 14.8
Blades: 3

Prop. Shaft Calculator _________________________________________

Prop. Shaft
Diameter: 1.375in
Material: Stainless 304
Shaft RPM: 4200 / 1.9:1 = 2210
Safety Factor: 2
Maximum Power: 179 SAE hp. (=133 kW = 182 Metric hp)

Rossjo , for the record "19x17 or 20x16 cupped " is what you posted last time That why I listed that ( copy and paste ) , I assume you used 16000 lbs then and 18000 now but we are close .

Maybe even try a 18x18 ? I would not go any smaller dia. my self

Didn't you say earlier your tachs where off ? did you ever fix them ?

I do not use the 1 inch rule as it can be way off

Not sure what you mean by "last time", but I used 18,000 all along, and simply posted the same results (as before). These are the original calculations, run months ago.

200RPM/inch is a good rule-of-thumb, used by many, so I use it as a starting point. Love to hear your rule-of-thumb ...

Tachs verified with portable tach attached to distributor.

Bottom line: Larry would like to find someone with a pair of used props in the 19-20 diameter and 16-17" pitch range for 1-3/8" shafts (or 1-1/2" as he can use shims).

Anyone have a pair sitting around gathering dust?

alexander38 wrote:I've got my popcorn.....

I'm glad I had time to get my sweet tea.....oops butter's done...

Thanx for the response guys, Ross is correct this time I did mis-state the prop sizes. I wonder if my boat was really going 2500 mph at 18 rpm. Hope everyone is enjoying to show, now play nice boys! Larry

rossjo wrote:Not sure what you mean by "last time", but I used 18,000 all along, and simply posted the same results (as before). These are the original calculations, run months ago.

200RPM/inch is a good rule-of-thumb, used by many, so I use it as a starting point. Love to hear your rule-of-thumb ...

Tachs verified with portable tach attached to distributor.

Bottom line: Larry would like to find someone with a pair of used props in the 19-20 diameter and 16-17" pitch range for 1-3/8" shafts (or 1-1/2" as he can use shims).

Anyone have a pair sitting around gathering dust?

Last time post read your numbers
http://www.trojanboats.net/wforum/viewt ... ght=#42637

Rule of thumb ? I don't have one as 1" of pitch change can have diffrent amounts of rpm change depending on size of prop , rpm of engine and so forth . Thats why I don't use it .

But we agree he is way over proped and are pretty close in numbers , whats a 1"

Man, you do love to dig ... yes, it turns out that I must have made the initial prop calc run using 16,000 lbs, which resulted in a different prop (19x16).

Are you married?

rossjo wrote:Man, you do love to dig ... yes, it turns out that I must have made the initial prop calc run using 16,000 lbs, which resulted in a different prop (19x16).

Are you married?

your started with 18000 , change it to 16000 ( trojans listed weght ) that was in your own words and know back at 18000 .

You really should fully read your posts ( and others ) Digging ? Not really I was looking at the history on this issue . Pay back ? could be LOL

BTW your intial cal using 16000 was 19x17 or 20x16
quote " Your 20x20 cupped 3-blade is overpropped - recommends 19x17 or 20x16 cupped 3-blade."

Read your posts or do you need glasses

married ? sorry not your type