F36 underpropped?

Allen Sr · Post by **Allen Sr** » Mon Feb 21, 2011 5:27 am

I checked my props last week end on my F36. Not sure what my gear ratio is but the props are 20x21. I have 350hp, 454's.

prowlersfish · Post by **prowlersfish** » Mon Feb 21, 2011 6:18 am

most likey 2 to 1 , but your engine gets its power at a much lower rpm

alexander38 · Post by **alexander38** » Mon Feb 21, 2011 3:58 pm

And 454' s make more over all torque

Allen Sr · Post by **Allen Sr** » Mon Feb 21, 2011 5:25 pm

The way mine is set up I have no problems getting up on plane. Give it a little throttle at a time it goes right up no struggling at all. Fuel and water tanks topped off loaded down.

alexander38 · Post by **alexander38** » Mon Feb 21, 2011 5:48 pm

As it should be, not taking a shot at SB's but I'd want BB's in a 36' boat. And #2 oil burners would be better, 36's can be a lot of boat to push once they get loaded down and if you have an aft cabin it's even heavier.

Allen Sr · Post by **Allen Sr** » Mon Feb 21, 2011 6:24 pm

I don't understand it. Sedans,convertibles,sportfishermans all seem to have big blocks in the 36 footers but the tri's seem to be all small blocks. Is that cause they are to hard to get out of the cabin area?

prowlersfish · Post by **prowlersfish** » Mon Feb 21, 2011 7:47 pm

they offered small blocks in the F36 conv but its very rare , and they put big blocks in the tri also rare , speed seems to be more important to the sport fisherman type boat (F36 conv) then the tri thats a cruising type

Just don't tell RB as he thinks the tri-cabin is a fishing boat

edrhathaway · Post by **edrhathaway** » Tue Sep 20, 2011 12:46 am

I'm turning 20x21 with 454 mercs running 20 at 3200 and 30 at 4400

rossjo · Post by **rossjo** » Wed Sep 21, 2011 1:38 pm

alexander38 wrote:And 454' s make more over all torque

Torque is king. HP ratings don't mean near as much as torque.

prowlersfish · Post by **prowlersfish** » Wed Sep 21, 2011 7:10 pm

rossjo wrote:
alexander38 wrote:And 454' s make more over all torque
Torque is king. HP ratings don't mean near as much as torque.

HP is the bottom line. tourque and HP hand and hand the right gearing changes everything , there is more to it the just torque , I have as much Torque at 1000 rpm as a big pig at max . But I sure need more then idle .

What would be faster a boat with 500 lbs Torque at 2500 rpm 1 to 1 gear or one with 250lbs Torque at 5000 rpm 2 to one gear ? what one would turn the bigger wheel ? need the biggest shaft ? the highest HP ?
Everything else being the same !

I can't wait for the answers

yes I am having some fun

alexander38 · Post by **alexander38** » Thu Sep 22, 2011 5:09 am

omg your trolling old post to have fun pickin' fights...and the seasons not over yet...

but high horse power gets you nothing with out lots of torque ..but lots torque doesn't need HP

Allen Sr · Post by **Allen Sr** » Thu Sep 22, 2011 5:56 am

My answer is the boat with 500lbs torque@2500rpm. It would require the bigger shaft and wheel and ultimately have the higher horsepower! Now how dumb am I?

Tony PLEASE keep your comments held off til later, at least til 0615!

prowlersfish · Post by **prowlersfish** » Thu Sep 22, 2011 6:43 am

alexander38 wrote:omg your trolling old post to have fun pickin' fights...and the seasons not over yet...
but high horse power gets you nothing with out lots of torque ..but lots torque doesn't need HP

I am not the one that brought up a old post commodore . but I find this a interesting discussion .

Do you know what HP is ? Allen your incorrect .

Torque x Engine speed) / 5,252 = Horsepower

rossjo · Post by **rossjo** » Thu Sep 22, 2011 7:44 am

prowlersfish wrote:
rossjo wrote:
alexander38 wrote:And 454' s make more over all torque
Torque is king. HP ratings don't mean near as much as torque.
HP is the bottom line. tourque and HP hand and hand the right gearing changes everything , there is more to it the just torque , I have as much Torque at 1000 rpm as a big pig at max . But I sure need more then idle .

What would be faster a boat with 500 lbs Torque at 2500 rpm 1 to 1 gear or one with 250lbs Torque at 5000 rpm 2 to one gear ? what one would turn the bigger wheel ? need the biggest shaft ? the highest HP ?
Everything else being the same !

I can't wait for the answers yes I am having some fun

Since you picked up the bait, I'll go ahead and set the hook.

Your question misses the point. The reason "torque is king in a boat" is because the larger displacement "torquey" engine has a fatter power curve - meaning it develops its peak torque at a lower % of its peak RPM, and has more torque throughout its power band. The less torquey engine will have less toque throughout it power band and develop its peak torque closer to its peak RPM and HP.

This is important in a boat, since you have a fixed gear ratio and a lot of weight to push through dense water. In a car for example, you have gears to shift to keep the RPMs up nearer the peak torque for acceleration/performance.

I'll pose back a more interesting question:

Given a 36', 16,000# semi-planing hull, which pair of 300hp rated engines would be the best choice for cruising on plane and top speed, assuming each was equipped with its optimum gear ratio and propellers:
1) Pair 7.4L, 300hp, 4,500rpm, V8 gas engines
2) Pair 5.9L, 300hp, 2,500rpm, L6 turbodiesels
3) Pair 5.7L, 300hp, 5,000rpm, V8 gas engines
4) Pair 2.6L, 300hp, 8,000rpm, L4 "tuner" gas engines
?

Why?

When it comes to diesel, torque is achieved at a much lower RPM, giving a more usable power range for a heavy boat:

Here is a good graph comparing gas versus diesel for example:

hmc · Post by **hmc** » Thu Sep 22, 2011 8:24 am

yOur chart must be from a diesel engine add , yest diesels is better boat engines on larger boats but the gas engin will aclaratel faster , this is a real wold fact . it takes time for the diesel to spool up

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F36 underpropped?

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