2 x 300 hp on a 5.5mtr rib. OH YES !!!!!

[Sonar]

Well not really..

I was looking on the net to see if there is a hp to boat size formula .

Building a 5.5 rib home build and thought a 150hp extra long shaft would do the job.
No make of vessel .Splash.

The transom is 60mm Solid well over the top reinforced and what with rear pods and a big knee bracket support's to 20 mm from the top of the transom.

Well over the top specs . weight not known yet as it is still to complete.
fuel tank volume should be around 180 ish ltrs.

so how does one decide on hp for the vessel.
an extra long shaft engine is required due to transom height.

[chewy]

Any idea of the weight?

Something around a 115hp should do?

[Poly]

this thread might be useful http://rib.net/forum/showthread.php?...hlight=formula

[Sonar]

Originally Posted by chewy

Any idea of the weight?

Something around a 115hp should do?

Not yet i am going to have to finish it first before i can weigh it.
but the length should be 5.4 to 5.5.

a little heaver than most I expect due to the layup and hard nose.
along with a higher freeboard of 150.

[Bigmuz7]

Depends on the weight of the hull but 135 would be about right IMO

[Sonar]

Originally Posted by Polwart

this thread might be useful http://rib.net/forum/showthread.php?...hlight=formula

Very useful many thanks
Robert

[Lets go boating]

a 90 opti goes well on a 5.5m lights well balnced great setup

[Sonar]

Originally Posted by Martha Focker

a 90 opti goes well on a 5.5m lights well balanced great setup

I had on the last rib I owned twin 50s on a 5.6 and that was 30 knots.
Thinking 150 may push what could be a heavier rib about the same speed.

But due to illness when it's completed i will be able to see how fast it goes.But won't have a go.

[Downhilldai]

As a guide for you, the 5.5m Vipermax is rated to 135hp and the 5.5 Northcraft is 150 hp

[Sonar]

Originally Posted by Downhilldai

As a guide for you, the 5.5m Vipermax is rated to 135hp and the 5.5 Northcraft is 150 hp

This one is well over the top on construction.
So I am thinking the 150 and see how it goes.
Having said that It's not a vessel I will be going in so it's up to Rob whom owns it what he will put in .

But many thanks for the valuable information.

[Bigmuz7]

Even with a 135 it will probably chine walk, but with a 150 ..

[Nos4r2]

Originally Posted by Sonar

I had on the last rib I owned twin 50s on a 5.6 and that was 30 knots.
Thinking 150 may push what could be a heavier rib about the same speed.

Errr, probably closer to 45/50!

[Sonar]

Originally Posted by Nos4r2

Errr, probably closer to 45/50!

No 28 knots 4 persons onboard according to a gps

30 knots 2 onboard

[Sonar]

Originally Posted by Bigmuz7

Even with a 135 it will probably chine walk, but with a 150 ..

What are the symptoms of chine walk ??

what happens when chine walk ??

[Nos4r2]

Originally Posted by Sonar

No 28 knots 4 persons onboard according to a gps

30 knots 2 onboard

Didn't mean your Avon-I was referring to this bit,which will be a lot more than 30 knots:-

Originally Posted by Sonar

Thinking 150 may push what could be a heavier rib about the same speed.

[Nos4r2]

Originally Posted by Sonar

What are the symptoms of chine walk ??

what happens when chine walk ??

This:-
[YOUTUBE]v9Yvj1FPR3s[/YOUTUBE]
The violent tipping/shaking from side to side most noticeable from 1.00 onwards.

[Sonar]

Originally Posted by Nos4r2

Didn't mean your Avon-I was referring to this bit,which will be a lot more than 30 knots:-

Hope so myself and the owner would be well pleased but just seen something about chine walking that's bothering me a little now as I fitted a large planing pad going by other posts answered on questions I was hoping porpoising and the walking would be out of the equation

Picture of the hull upside down showing the pad.

Hoping now I have not made a big mistake or I will have to start another one.

[captnjack]

Just about any monohull is going to chine walk once its getting airborne like that little green boat in the video. If anything your large-ish planing pad will actually moderate it some since the hull won't be "flopping" back and forth across the deadrise.

[Bigmuz7]

Wow .. the bit you have as the 'planing pad' is normally the only bit of the deep V hull left touching the water when chine walking starts .. so all you've got here is a flat section touching the water at full speed at exactly the angle the water hits it .. Hehe... thats gonna be interesting with a 150 .. Chine walking only happens when enough hull is out of the water when under way at high speed, so balance becomes critical, and when the sea is flat enough, hull contact becomes minimal and over she goes, or when a regular chop dissapears as you enter a flat area round a point for example, hull contact reduces suddenly at a regular fast speed, and over she goes unexpectly.

If you have enough ballast, and trim options, you can mostly correct it .. so dont panick .. but the simpler answer is to not overpower the hull, or trim and throttle back

The Vid Nos posted above does show it, but nothing like the violence I have experienced, in a deep V hull where on a light 5.8M with a 135 it nearly threw us out of the boat when it slapped from side to side unexpectedly

I have owned a hull where the planing pad was rectangular on a 6.3M and didnt have any problems, but the boat was much heavier with a 150 so was not over powered

[Sonar]

Very interesting So I guess the answer is not to over power.
I am hoping the rib will be quite heavy when loaded .

So would it be better to make another hull with out a planing pad .????