Naumacos 25 Racing Rib

fede · 21 June 2006, 17:08

Hi everyone, I'm new to the forum, my name is Federico and I'm a designer from Milano Italy.
In the last 8 months I've been working on a new RIB specifically intended for racing and sport activities,the Rib first "bath" have been on friday june 16th and results have been very satisfactory, it already reached 70 knots with engine at 5200 rpm, engine will be capable of 6000 rpm,and a change of prop height is now needed to let the prop work more on the surface.
The RIb is a prototype and will be racing in the italian Endurance circuit.
Attached some pics,any comments,suggestions or critiques are welcome.
Sorry for the low quality of pics.

jimc · 21 June 2006, 17:11

Good looking boat, what engine/s do you have in there???

fede · 21 June 2006, 18:03

Thanks,as far as engine...nobody really knows...it's a mercruiser 7.4 engine (454) ,of the original engine just the block is still there,while everything else has been "upgraded" it probably dlivers something betw. 400 450 hp.
Leg is a "regular" bravo 1,a -2 lower unit would be put on soon as it is neede.

Bou · 21 June 2006, 18:16

Welcome!

First of all, its a stunning looking boat!

Second...on the third picture it really looks like a Revenger....??

Gr,

Bou

codprawn · 21 June 2006, 19:34

Looks stunning - hull looks familiar though....

fede · 21 June 2006, 20:42

Ok guys, a Leeway a Revenger next?? a Buzzi? an Effelle? A Pascoe?
To all of you that are undecided which Hull i copied from the discussion is moved to:
http://www.rib.net/forum/showthread.php?t=14911
I?m trying to defend myself there, sorry but I'm not used to fight on 2 different fronts at one time...

I've been working on this for 8 months but I'm already thinking that it's been all wasted time...

aphro · 21 June 2006, 21:39

looks great
should come and race at the red sea rib rally

fede · 21 June 2006, 21:55

Thanks Aphro!
I searched a bit about Red Sea Rally, it sounds great!
I will inform the team about that,it is probably a very expensive race though.

Cookee · 23 June 2006, 10:08

The cost for the 200hp class is £3,500, but that includes flights and accomodation for 3 as well as fuel along with TV coverage of the event - it will be a high profile event and a fantastic opportunity! We are taking part along with most of the UK racing RIBs.

fede · 23 June 2006, 10:34

Price is not that high.
WOW, the Banana Shark is great Rib,congrats!!!
I like the tubes profile a lot also,having a very fine bow entry I was afraid that making tubes to thin at the bow would have gave me nose stuffing problems.

What other Racing Ribs are involved?

Can you give me some Banana numbers? (weight,speed,dimensions etc.)

fast fred · 23 June 2006, 17:31

looks a bit wet runnin, that mite change with a dif' foot on it, a numbered foot, will it be capable of triple outboards? how do you think She would hold up with an SC900 in it?

fede · 23 June 2006, 18:59

Yes you are right Fast Fred,I think that the excessive water is raised by the two trim tabs that are positioned aligned with the hull bottom, next thing we are going to do before we even raise or change the leg is raise the flaps and put them aligned horizontaly.

And no, I think 900 hp from a single engine would be too much for this boat.
I think that 600 650 would be a "safe" and performing choice.

SHe might be able to hold 900 hp but I wouldn't have the guts to be the one who try!!

fast fred · 23 June 2006, 21:23

with outboards, triples, they would cancle out most of the torque,
seen a twin foot set up on a inboard drag hull (think it was about 18' , with a nitro big block SC motor, ? 4500hp+) the twin foot set up cancles out most of the torque, keeps the transom from crabin when the power hits.

hows the torque roll with the big block? dose she lean hard?

fede · 23 June 2006, 22:41

I'd like to see it with twin 2.5,I guess the twin engines would be fine as far as torque is concerned, 3 is not necessary.
She does lean a bit while planing with a 25 prop but not always the 25 is too short anyhow, perfectly straight with a 26,I'm pretty shure a 27 would be the perfect prop,but first we have to raise the leg 1 inch,a SSM leg would be the right thing here.
We achieved 79mph with a 26 but I'm shure there is much more with the same engine,we did 76 with a 25 and the pics you see are with the 25.

Bottom is too low into water and we need to pull it out,once it "frees up" from excessive water she'll pick up a lot,we need to experiment with appendages (leg height,trim tabs etc) and some weight shifting to get the correct balance,hope we don't need to move the gas tank forward,with weight distributed this way the long stability is perfect,no porpoising throughout the all spectrum of speeds.
Next trial we will try no trim tabs at all and see how she behaves,it's been a mistake to put trim tabs before first trial,lesson learned...
I'll be satisfied at 85 mph although I'm shure it can get to 87.
I?m more concerned about stability and balance than about max speed.
It's better to run at 82 steady than at 85 once in a while...

Cookee · 24 June 2006, 10:33

Quote:

Originally Posted by fede

Price is not that high.
WOW, the Banana Shark is great Rib,congrats!!!
I like the tubes profile a lot also,having a very fine bow entry I was afraid that making tubes to thin at the bow would have gave me nose stuffing problems.

What other Racing Ribs are involved?

Can you give me some Banana numbers? (weight,speed,dimensions etc.)

We have raced very succesfully against Bat boats in class 3C, althouth they are faster in flat conditions our hull is much faster in the rough, especially downwind where it is outstanding! You don't need tubes to stop a boat stuffing - how do you think hard boats manage it?

I believe if you rely on the tubes to keep the nose out you will have trouble keeping the tubes on - especially with larger boats - the big Scorpians all have hard noses for this reason now!

As far as the UK boats are concerned they are mostly Pascoes which were originally batboats from Mannerfelt built under license I believe. Recent report from Egypt:

Quote:

The weather conditions were interesting with sand storms, 50 plus knots of wind and some 4 meter seas running in the Red Sea

I think you can safely say I'm looking forward to some interesting conditions!

Numbers for the race BananaShark: 7.4m hull length, 2.5 beam to the outside of the tubes, 960kg, Mercury XS200, 73mph in race conditions - 75mph max at the moment! 150 litre bow tank. We also make a leisure 5 seat version which is running at 65mph with a Verado 250.

fede · 24 June 2006, 11:21

Hi Cookee,My rib is 2.5 wide at the tubes and 1.9 at the chine,how beamy is yours at the chine?
Your boat is extremely light,our boat is 1400 kg,just engine and leg weight more than 550 kg.
Do you have trim tabs?
How many hp is your xs200 capable of ? I mean is it modified?
I would like to try mine with a single outboard and with two counter rotating outboards,may be 2 x 2.5 xs same power with less weight (almost 200 kg less)
We are going to test a - 2 shorty on our leg on fryday and see what happens...hopefully it will get onto plane...
Also we are going to straighten a rounded corner the builder made under the transom,I?m afraid that water turns around it and gets thrown high.
I'll let you know...
Those of the red sea are indeed interesting conditions !!!

fast fred · 25 June 2006, 12:53

workin on this one, guna make some test pulls before tabbin it, will put a water tank in the bow with athrough hull pickup so she can pump and or dump
the tank as needed to keep her attitude in check.

Cookee · 26 June 2006, 15:27

Quote:

Originally Posted by fede

Hi Cookee,My rib is 2.5 wide at the tubes and 1.9 at the chine,how beamy is yours at the chine?
Your boat is extremely light,our boat is 1400 kg,just engine and leg weight more than 550 kg.
Do you have trim tabs?
How many hp is your xs200 capable of ? I mean is it modified?
I would like to try mine with a single outboard and with two counter rotating outboards,may be 2 x 2.5 xs same power with less weight (almost 200 kg less)
We are going to test a - 2 shorty on our leg on fryday and see what happens...hopefully it will get onto plane...
Also we are going to straighten a rounded corner the builder made under the transom,I?m afraid that water turns around it and gets thrown high.
I'll let you know...
Those of the red sea are indeed interesting conditions !!!

I am informed by someone better at measuring things than me (Kitten) that our boat is 1.97m at the chine.

As far as weight goes, rather than a heavy inboard, we have a alluminium bracket, a Stainless Marine lifter and a relatively light Merc XS200! The engine is standard - we are not allowed to modify them at all, so 200 hp is all we get!

No tabs on our boats - I was tempted to try some, but the ones I got were a bit too big to fit! (and quite heavy as well!).

Look forward to seeing how you get on - looks a great boat!