Hull Design - Which is better?

Chris Murray · 14 August 2003, 22:34

There was a very long article about hull design in RIBs International this month. Having got to the end of it, I have to say that I am not really any wiser about this subject!

As far as I can see, there are long pointy boats, such as Scorpions, Revengers, etc. and there are more traditional RIBs, such as Ribcraft, Ribtec and the like.

Until Saturday, I felt that the traditional style was likely to be more appropriate for my own purposes, but seeing the wide variety of boats out to welcome SoP - and the relatively few traditional models - causes me to review my thinking.

When I eventually get my boat, it will be in the 7.5mtr to 8.5mtr range, with (most likely) a 300HP Vmax, Yes - these have now been announced for 2004. I haven't completely closed the door on diesel but I still need a lot of convincing!

I intend to use the boat both for Channel hopping and for relatively high speed "spins" mainly in the Solent.

Since the RNLI tends to go for traditional styles, I should have thought that such boats could better handle "difficult" conditions and are presumably more "comfortable" (OK, I know that this is relative!).

I am keen to hear your views on the relative merits of your boats, why you chose the particular hull and engine configuration and if you would buy the same again, having experienced it.

I look forward to hearing from you!

Regards,

Chris.

John Kennett · 14 August 2003, 22:52

How fast do you want to go? How important is top speed?

For offshore cruising a deep V hull is generally going to be best (although it may be worth considering something less conventional such as a Hysucat) but they take a lot of power to go really fast. That Scorpion I was driving at the weekend does about 50 knots with twin 200s on the back.

For long distance cruising you will probably find that you average 25-30 knots whatever, although a 40 knot cruising speed is great for really covering some ground when the weather is good.

I'd say that you are looking at the right size of boat for something that is easily manageable afloat and on shore.

In your position I would go for an 8.5m RIB (Ribtec, Scorpion, Ribcraft) with a 300+ hp diesel. This will give a top speed of (guessing) 45 knots, and comfortable cruising at 30 knots. Why are you so keen on an outboard?

John

Chris Murray · 14 August 2003, 23:19

Hello John,

Good to meet you at the weekend!

I was hoping for around 50kts plus as, somewhat surprisingly, 41kts in a 7.5mtr RIB actually seemed slower than 36kts in my last boat (Falcon 23 SPC). I really wanted any new boat to "feel" as though I was going faster!

I have to admit to being keen on anything "hi-tech" and I don't think you can get much more hi-tech than the current crop of high-powered 2-strokes. Diesels do seem to take up a lot of boat space, so - in the current "sporty" ranges, I would probably be looking at an 8.75mtr Scorpion or a Revenger 29. Conventional-style boats seem to have a few gaps at this length, with either a 7.8mtr commercial RIB or an over-sized (width-wise) 9mtr in the Ribcraft range.

Until recently, I was looking at boats under 8 mtrs, which were generally too small to accommodate a diesel much over 230HP, which I consider would not give me the performance that I am looking for.

I have also concluded that a "deep V" is needed, but it is difficult to distinguish between the makes that you mention. However, those that appear to have a racing heritage (e.g. Scorpion, Revenger), whilst likely to be a deep V, have a very different bow configuration to the more conventional "rough weather" RIB, such as an Atlantic 21. Logically, there must still be merit in the conventional design, or the RNLI would have started using the more "racey" looking models.

Hence, I am keen to hear from owners, to establish the pros and cons from people who use the boats, rather than just "sell" them.

Thank you for your thoughts!

Best wishes,

Chris.

Julian · 15 August 2003, 10:33

Hi Chris

We have a 8.,5 Scorpion with a 300hp Yanmar diesel engine, we get a top speed of 47knots, the hull is very good, i have covered thousands of miles in this boat in some very rough seas and it performs amazingly well, its a soft dry ride ( most of the time ). We have a hard nose as well which breaks the waves in a following sea and helps to maintain a high average speed. The same goes for Ribtec and revenger, i have been in heavy seas in both of these boats and they perform well, In my view the Ribtec was better in the rough than the revenger. Hope this is of some help.

Julian

Chris Murray · 16 August 2003, 23:03

Thanks Julian,

This is just the sort of information that I was looking for.

It looks like I might have to explore diesels then.

Actually, one of my concerns was having another sterndrive - On my last boat, I used to remove this every year, change bellows etc., which represented a lot of maintenance. This was another attraction of an outboard for me, as it does not have to remain in the water, even if the boat does! (should = less maintenance).

I am also concerned that I could buy a diesel, accept less "sparkling" performance than I might wish for and then find that the price gets close to petrol. Low running costs would be a good reason to use diesel - especially as I want to cover some reasonable distances - but with all the unknowns about 2006, this might prove to be an unsound reason for purchase.

I am certainly interested in the view that diesel powered boats run more level and are therefore better in the rough (perhaps) - again this is the type of information that could justify going down this route.

Thanks again for your input!

Regards,

Chris.

Arek Pawelek · 20 August 2003, 17:51

On www.parkerribs.com you can find what you need, I think. Sizes from 5,4 up to 9 m.

John Harding · 26 August 2003, 19:17

Hi
I am slightly surprised that in the replies to your query no-one has mentioned high volume bows like Delta or Humber boats provide. I am thinking of buying a RIB too in the size range 5.8 -6.5 with about 120/130 HP 4-stroke outboard and have been steered by friends to look at Delta or Humber boats. Can you or anyone offer any advice especially on the question of high & high volume bows? I think it is clear (at least to me) that deep v hulls with the V running right aft are best but I might be wrong. I want to know that when it gets unexpectedly rough or a return passge has to be made in bad conditions the boat will not let me down!
John

Pete7 · 27 August 2003, 09:12

John, its is quite possible to stuff any rib including a Delta if you get it wrong eg down the waves and close the throttle at the wrong time. Been there and done that. There is a marvellous saying of "throttle with bottle". As for hull design and shape hmm I think everyone has there own favourite. I liked the warped V from Osprey (formerly Fletcher in the distance past). Perhaps you should borrow a deep V rib for a day, fancy a Ribtec 6.45 ?

Pete

Arek Pawelek · 27 August 2003, 09:25

First, when going down wave - High volume bow dont let the bow to dive, but if the tubes are not to small (diameter) or the front of the boat is not overloaded, then high volume bow is not necessary.
Second - going up waves, with high volume bow riding is very "bumpy", and may even finish up-side-down. I had seen such thing two times! Unexperienced pilot pushed throttle a little too far, and sent a boat flying. The only thing, what you can do with the boat with high volume bow is to put a lot of load on the front of the boat. RNLI guys have on their ribs a tank full of water only to start from the beach. After start tey are emtying the tank to make bow lighter.

Cheers!

Arek

gtflash · 27 August 2003, 16:14

im also considering a 7.5m ish size rib. Its interesting that nobody ever seems to mention either zodiac, or phantom ribs. I know zodiac have dep v and big tubes, the phantom i just like the look of and know very little about. Only today a dealer for many ribs (except scorpion) said that if i really want a serious rib then scorpion is the best in uk without a doubt, and he doesnt even sell them....! I understand not wanting a stern drive, mine has cost a fortune. I will be after the biggest 4 stroke outboard (its a comprimise i believe).

Maybe pete could clarify something for me about throttle. My boat (non rib) has a very firm throttle and its almost impossible to throttle on or off slightly without serious drop in power especially as the boat is a deep stepped v and it digs in. As a consequence sometimes its an ouch experience. Silly question and off subject a bit but id appreciate any throttle technique tips and does anyone know if i can adjust it and roughly what is optimum firmness!! Its a quicksilver throttle

Pete7 · 27 August 2003, 16:30

Throttles then. Arek is quite right, about going up and down waves, (we are talking offshore rather than the Solent chop which normally defies any technique other than just go for it). You will notice that with the power on the bow rises and when the power comes off the bow falls. So going down the waves put the power on which helps lift the bow and stops it stuffing. If you take the power off the bow drops, as does the speed and you run straight into the back of the next wave. Boat stops and you are in danger of broaching the boat from the wave that is now coming up from behind you. Big waves move very fast. Going into the waves take the power off just as you get to the top, the bow drops and the boat rides over the wave without going air bourne, but its all about timing and you will never get all the waves right so expect the odd "oops".

The standard side mount throttles with most outboards are "bonk" and don't allow the driver enough finese, try holding the lever stalk rather than the top of the handle. The friction controls also leave something to be desired. Next time you see someone with top mount controls ask to have a fiddle with his levers to see the difference.

Pete

Arek Pawelek · 27 August 2003, 16:46

Other technique, which I used, going with the wave, was not fiddling with throttle, but with steering wheel. On top of the wave I slightly steered off to dont go directly down, but to make kind of side-slide. It was working really good. And without changing reevs all the times, the amount of petrol used by engin decreases. BTW, conditions at this time: wind force 10, waves 2-3 m, quite short and steep (Baltic Sea). RIB 4,5 m with high volume bow, 60 HP Mercury

Arek Pawelek · 27 August 2003, 16:59

gtflash wrote: "im also considering a 7.5m ish size rib. Its interesting that nobody ever seems to mention either zodiac, or phantom ribs. I know zodiac have dep v and big tubes,..."

I used Zodiac PRO II, which has deep V bow, and riding of this boat was really nice! Either down waves, and back, up-waves. Size of the boat was 4,5 or something like that. Later I had a few rides on Bombard Explorer 6 m, 90 HP Evinrude. Very good boat. And again, deep V bow, and high volume tubes. Much more comfortable ride, than on other boat, which I used (Sportis 6,1, 115 HP Evinrude), which has high volume bow.