Where should I start

[old bird]

Old Formula Thunderbird 26' x 9'6", 1977
twin 454/330hp TR drives ,1:5 ratio
Heavy boat, dont know the weight, wish i did. (6-8000 + ???)
What prop would you say to try?
It's got 20"x15p alum. on it now. I'm sure this aint right,
Don't ask wot rpm, can spin them to over rev.
Any thoughts ???

Thanks

 

[hwsiii]

Re: Where should I start

Bird, you did not tell us the RPM developed by those motors. I found your boat to weigh right at 7,000 pounds dry, I figure 150 gallons of fuel and 3 adults with two children and assorted normal gear for a boat that size a minimum allup weight of 9,000 pounds. I also need to have a better idea of the speed and RPM you are attaining at this point in time. It is crucial to my calculations, I have a Boat and motor info sheet as well as a Prop test sheet if you really want to find the correct props for your boat. I have filled out a preliminary Boat weight and Motor info sheet for your perusal, but I do not know if the RPM are correct. I will also post the Prop test Sheet, and if you want these forms to fill out for my calculations just send me your email address. Without the correct information it is impossible for me to calculate the corret props.

H

 

[old bird]

Re: Where should I start

Just for kicks,
what would you all try if you had no basis for comparison?

26' , 8000lb. deep v, twin 330hp., rated to run 42-4800 rmp,
1.5 drive ratio,
What would you suggest to try ?
a ?x? or a ?x? etc.

 

[steelespike]

Re: Where should I start

You should read the stickies at the top of the page and the helps at the prop store page.From my research it appears you have your numbers reversed on the prop size.Should be 15 X 20.Is it 3 or 4 blade?
It would be better if you could be more specific on your present max rpm.
Also would be good to have the speed at rpm to get some kind of idea if the present props are working to specs. Are you over reving at 1/2 throttle 3/4?
is it climbing right on to 6,000 or perhaps 5,000 5,500?If the moptors are healthy you could run it momentarily if its 3 or 400 over.
What is the max rated rpm?(usually on a label on the motor).

 

[old bird]

Re: Where should I start

This Boat has 454 c.i engines, 330 hp.each, they are Big Block engines, rated to run 42, 45 up to 4800rpm wot.
It has Inboard MerCruiser transmissions, 1-1 ratio, TRS drives ,upper,
w/TR (Big Foot) lowers. 1.5-1 ratio.
It HAS 20" diameter alum. props on it with 15' pitch.
These props cant even be close to right. This set up is for a house boat or barge LOL.
Long (ugly) story why these over size drives and props are on it.
But that's what i got.
I was hopeing for some suggestions, what to consider, IF, i come across
something. Thought some one had a formula that says, whith this package, a ?x?, or a ?x? should do this that or another.

Thank anyway.
Larry

 

[hwsiii]

Re: Where should I start

If you gave us some speeds with RPM we could help.

H

 

[old bird]

Re: Where should I start

Thanks.
I'll get some kind of speed readings and rpm's back to yuo.

Funny how things happen.
I got my old drives back this eve. with the props
Quisksilver 48 13704 A40 23P

 

[rufusgrouse]

Re: Where should I start

Tr/trs is all I do, www.kcmarinetr.com Call me with all the particulars and I will steer you in the proper direction.
These old wardogs refuse to die. We have shipped to Australia, Italy, Hong Kong, Sweden, Germany and more. They are one of the most desired designs Merc has ever come up with; but certain design issues demand attention. No charge whatsoever for any advice you might need......