15.5ft Rana 16 Line (DC) + 90HP Mariner. Spitfire X7 21P good choice?

[GreedyMuffin]

Hi!

I have a Norwegian made boat, under 50 made. It's called Rana 16 Line and it's from 1970. Pictures of hull and top. (The boat will get a updated antifoul soon, before I release her out on the ocean again. But she dosen't look bad to be 47 years! Bought her last summer)

4.75M long, 1.98M beam and once it weighed 375 KG without engine etc. I guess the weight without people is between 560 and 600 KG, including gasoline and the engine.

Gear is 2,33:1. HP is on engine 90. I guess I will be sniffing on the 40 knot range with this boat/engine

I have the chance to spend some extra money and getting a barely used Spitfire X7 21P SS for my boat/engine. I get it a few hundred below store-price. So I am really considering to grab it.

 

[SkiDad]

It's hard to tell without testing, but that pitch seems reasonable to me given the weight of the boat. You might have to watch your RPM some. I'm not sure if your boat maxes out at 5250 or 5500

 

[GreedyMuffin]

So you believe that it would work good? I just don't want to RPM to be lower than 5000, and higher than 5500.

Recommended RPM for my engine is 5000-5500. The 75HP is 4750-5250

A 13.25 x 22 x 4 would be too much for my engine? Or is the 12.7 x 21 x 4 a better choice?

Thank you!

 

[GreedyMuffin]

I have two other props that can be exhanged back if they don't fit so good. They are used but are half the price each compared to the also used X7.

13.25 x 20 x 4
13.25 x 22 x 4

 

[Sea Rider]

In reality you need to test current 90 prop at wot as usually loaded, depending on wot rpm achieved, maximize a prop that will shoot wot rpm towards max 5500 range. It's a very bad investment buying props blindly without testing previous one as a starter prop.

Happy Boating

 

[SkiDad]

i got the impression that you had no prior prop to test with ? If you do, you need to do some tests and report back to us your rpm.

 

[Texasmark]

It's hard to tell without testing, but that pitch seems reasonable to me given the weight of the boat. You might have to watch your RPM some. I'm not sure if your boat maxes out at 5250 or 5500

5500. I ran mine 56-5800 most of it's life.....it loved it.

 

[jimmbo]

So you believe that it would work good? I just don't want to RPM to be lower than 5000, and higher than 5500.

Recommended RPM for my engine is 5000-5500. The 75HP is 4750-5250

A 13.25 x 22 x 4 would be too much for my engine? Or is the 12.7 x 21 x 4 a better choice?

Thank you!

That engine really doesn't like being over revved. 15 1/2 ft with a 3 cylinder 90hp? I would have said a 3 blade 19 in

 

[Texasmark]

Crap shoot: 21 too much prop. 19 would be better due to hull shape, and knowing you are going to load up with folks and water toys. ID of what you have and performance that others asked for will assist you in getting the correct answer to your question. I had that engine and had a 21 and the boat was much lighter, faster, flatter, easier planing transom, and no water toys. Really doubt you would be happy with it.

 

[GreedyMuffin]

Hi!

I decided to purchase a new, bigger boat. It's 5,65M long, 2,30M beam, 500KG dryweight etc.

I made a new thread about it, will use the same engine: http://forums.iboats.com/forum/gene...8-5-ft-alicraft-18-norwind-with-mariner-90-2t

Thank you all! The req. is the same.

Happy boating!