Polycraft setup.... what are your numbers?

[Blackened]

G'day

Mate of mine has just purchased a 480 Brumby cc, he's stoked!

It's powered by a Suzy 70 4 banger, prop is the standard alloy suzuki 15p, height of the engine is on it's lowest setting.... anti-ventilation plate is just on the surface at plane... but still looks like it could be lifted a hole to me (yet to do this).

The numbers are as follows.

WOT is now at 5400 RPM (bang on for this engine) with a top end of 25kts.

Cruise at 4000 RPM is 18 kts.

To me this seems slow... I'd expect it to be somewhere around 22 kts cruise and 28-30 kts top end.... Am I expecting too much?

Who else is running the poly's with a similar setup (480 and 70hp)

What prop do you run and what are your figures?

Dave

[Giffo65]

I have a 4.55 with a 60 Yammy four stroke high thrust and get 27 kn off the GPS at WOT.Be aware that 60 hp is max for those hulls,insurance may wipe you should an incident arrise.Great boat for their size,you could put up a post on Polyboatowners forum,you may get some info there.

[frankgrimes]

Hey Dave - 25knots is a bit slow, especially with a 70....Got the 4.5 drifter CC, 60 Merc 4 banger, and have squeezed ~31knots out of her.

As Giffo stated, they are only rated to 60(Unless he has had the hull re-rated?)

Mick

[chris69]

How deep is the cavition plat, that will tell you a lot if theres a lot of water over it bring it up a hole or 2 and change prop add a inch of pitch if the motor is going beyond max revs,with a 70hp it should be flying with a 60hp yammy as aboves post from griffo65 doing 28kts your mates rig should be doing 30kts or over for sure.

[TheRealAndy]

My 4.55 does about 25knots wtih yam 50 banger 4 stroke.

[Blackened]

G'day

Looks like i stuffed up.... boat is actually the 4.8 brumby! and I promise the rest is accurate.... see what happens when you return from south america? mind is elsewhere!

So those figures with the 4.8 and 70 suzy.... acceptable?

Dave

[frankgrimes]

Hey Dave - Check this thread out @ polyboatowners (You *may* need to sign up though) - http://www.polyboatowners.com/2010/vb/showthread.php?t=294

One of the posts:

"I have a 70 suzuki on my 4.8 and i get 32knots with the whole family on board. Seems fine to me "

but, Poly's LOVE max HP...the brumby(4.8) has been "re-rated" to 90...so if upgrade is an option, then go a 90!

Cheers,
Mick