Hunton/ilmor Build

peter unwin

Senior member
Joined
Sep 1, 2006
Messages
557
Location
East Mids
Cruising area
Southampton
Boat name
Cheetah
Boat make
XRS37 hunton
Engines(s)
twin volvo D6's
Here is progress so far on a stretched Hunton XRS37 to be fitted with staggered Ilmor 725's with the Indy drive
 

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Now this is a build thread I am interested in.

Keep em coming Peter. :up:
 
Oh, maybe Cinzano won't have it all their own way in Class B

Please keep the photo's going as the build progresses...... C U in the first Marathon race,

Dean
 
forgot how different the boat looked in red and black, keep the photos coming
 
Wow looks like a fantastic project, so great to see the sport all of us on here love growing, thanks to ML kicking of the RB08 and the rest of the dedicated guys pulling it all together for the Marathon series looks like next season could really be the start of something big or bigger even

Is this the same boat spoken about in this thread as this one was a production boat fully fitted out for that nice cruise to the IOW on a sunny weekend and it has port holes that are not in your above photo

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http://boatmad.com/forum/showthread.php?t=10046&highlight=hunton
 
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Peter isn't intending to race this boat, as it's been built pretty light and thus won't conform to the Marathon rules.
Just a very special (and fast) pleasure boat.
 
fantastic looking boat and looking at the inside hull pics looks very strong too
 
Awesome... What kind of speeds are you expecting with the Ilmors? Those Indy Drives are gorgeous looking bits of kit
 
Wow looks like a fantastic project, so great to see the sport all of us on here love growing, thanks to ML kicking of the RB08 and the rest of the dedicated guys pulling it all together for the Marathon series looks like next season could really be the start of something big or bigger even

Is this the same boat spoken about in this thread as this one was a production boat fully fitted out for that nice cruise to the IOW on a sunny weekend and it has port holes that are not in your above photo

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http://boatmad.com/forum/showthread.php?t=10046&highlight=hunton
Hi CFUN,
The all red boat in your picture is the one we have owned since march 2007 which has modified D6 volvos that has nearly 700 hrs on it in less than 3 seasons.
The red & black one is a completely new project.
The basis of which is a Hunton XRS37 extended by 750 mm. All of the extension is in the engine bay to allow plenty of room to stagger the engines & make an even better rough water boat. The hull & deck are constructed from kevlar & is incredibly strong & light as a result. The whole build process is to use materials strong but as light as possible.
One of the reason's for choosing the Illmors is their light weight.
The boat is being built to race specifications but as Jon has pointed out it will be too light for marathon racing.As we do such a lot of pleasure boating it would seem an awful waste to carry ballast to fit the marathon rules all of the time but i wouldn't rule out using removable ballast in the future.
Peter
 
Too light?

If the minimum wt limitation is 360kg/m (I take this is light load with 5% fuel left and including crew wt?),then something like Cinzano should be virtually right on it.
I would imagine the Hunton is beamer and with the accommodation fit out,it should be heavier (tupperware OPI were much the same wt as alloy OP 1),unless it`s built super lightweight and even if it is it would have to be designed to the same stress levels as Cinzano if it has 1450 hp in the Hunton,(Cinzano had 1400hp at one time).
So from the above the Hunton should be as strong as Cinzano so why let min wt be the guide to whether the boat is seaworthy or not (I take it that`s what the rule is there for,to stop lightweight flimsy hulls breaking up at sea).
It`s almost like saying a 37ft boat in the future can be built much lighter (but as strong) for the same power, but if it is it won`t pass the min wt rule unless we ballast it up?.I await to be enlightened (no pun intended)

If 1450hp were stuck in Cinzano it should in light condition do over 90mph .
 
Discouraging 'flimsey' boats was part of it, but also there was an element of levelling the playing field tween diesel and petrol boats. ie, min weights were guestimated on what a diesel boat might weigh, rather than what a petrol boat could weigh. (for a given power)

Writing rules is a ferkin minefield, and believe you me, the aggro continues to this day.
 
Rule loopholes

I had a feeling your reply Jon would be along those lines.It`s a thankless task and have I my own views on it as it stands,but that would open a can of worms I`m afraid,but generally the more one tries to compartmentize areas of boat design,the more snags it throws up.One question to ask before any rulemaking is why does one want to do Marathon racing,the elements,the sense of achievement,the competition,and if class definition comes out low in the priority,then keep it simple and use the minimum for flexiblity and future modification.You can never please everybody whichever way,so you might just as well keep it basic,so it`s easily understandable.
 
If the minimum wt limitation is 360kg/m (I take this is light load with 5% fuel left and including crew wt?),then something like Cinzano should be virtually right on it.
I would imagine the Hunton is beamer and with the accommodation fit out,it should be heavier (tupperware OPI were much the same wt as alloy OP 1),unless it`s built super lightweight and even if it is it would have to be designed to the same stress levels as Cinzano if it has 1450 hp in the Hunton,(Cinzano had 1400hp at one time).
So from the above the Hunton should be as strong as Cinzano so why let min wt be the guide to whether the boat is seaworthy or not (I take it that`s what the rule is there for,to stop lightweight flimsy hulls breaking up at sea).
It`s almost like saying a 37ft boat in the future can be built much lighter (but as strong) for the same power, but if it is it won`t pass the min wt rule unless we ballast it up?.I await to be enlightened (no pun intended)

If 1450hp were stuck in Cinzano it should in light condition do over 90mph .

Hi Flying Fish,
I believe the weight of Cinzano is in the region of 5.5 ton with a power to weight ratio of 236 hp per ton. The weight of the Illmor Hunton is at worst 3.7 ton un ballasted giving a power of weight ratio of 392 hp per ton.
The beam of the boat is 8ft 6" the boat consists of hull & deck moulding, fuel tank,engines & drives, trim tabs, light weight wiring & instrumentation and absolutely NO CREATURE COMFORTS!! I.E: BUCKET & CHUCK IT!!.On the subject of diesel versus petrol i believe the equivalence formula to be heavily biast toward diesel engines, using the Illmor as an example it has approximately 86 hp per litre, forced induction diesel engines are well capable of making more than 110 hp per litre.So as the petrol & diesel boats have to weigh the same the diesel power boats have a distinct advantage, but as a confirmed petrol head i know what i would rather have singing in the back of the boat!
Peter
 
i believe the equivalence formula to be heavily biast toward diesel engines, using the Illmor as an example it has approximately 86 hp per litre, forced induction diesel engines are well capable of making more than 110 hp per litre.

There are plenty of 100hp/litre gas motors (normally aspirated) and very few diesels of over 100hp/litre.

The full race 10.3 Seatek was only really 1100hp at best in reliable format (that's obviously needed for endurance racing) so only a little over the 100hp/litre and that's was a rare, expensive, purpose built race machine. The Volvo D6 5.5 litre is quite remarkable at 435 hp, certainly I would say 'the norm' at around 80hp/litre. Our Steyr's are closer to 100hp/litre (claimed) as are the new BMW based Yanmar BY's, but the larger production motors don't seem to find it so easy to approach the magic figure.

The latest Fiat 6.7's are 560hp (83hp/litre) and Fabio runs them higher at 600hp, so still under the magic figure. His (works sponsored) motive power surely must be a guide the realistic 'state of the art' for diesel power? They weigh 3/4 ton each, plus monster heavy gearbox's, batteries etc.

I'm not sure the power to weight ratio you've quoted a couple of times is as relevant in boating, as in your tarmac motorsports. I did see your question the other day re: the Levi formula, and will post some stuff, but it's a lot more complex with boats, as Flying Fish will agree I'm sure. so need to write an essay.
 
Hunton data

Hi Peter,

All interesting stuff.The weights you give out I would think are fully fuelled wts,based on Cinzano`s wt which I reckon to be more like 5 ton.No matter,crane wts can be a bit iffy,load cells I would rather trust.Working backwards from your data it would appear your lightship is nigh on 70% of a CUV 38,which really puts the cat amongst the pigeons rulewise,if it ever went racing.
I must admit a 38ft boat with 1450hp and with that sort of lightweight in race conditions seems getting on the hairy side,considering they reckon a CUV38 travelling over 90mph is becoming a bit unstable,even lightweight U.S. monos are a bit longer to handle that sort of power.There was the CUV 38 San Benedetto which had 1640hp,but that was regarded as on the limit.
As you say, the boat is for pleasure use,assuming the owner is comfortable with that sort of power.
When it comes to comparing the relative merits of diesel v petrol,that is another variable which makes the rulemaking so difficult,and hence to my mind the need to be flexible to avoid the rule loopholes.Take a entry list from many years ago and see the range of horsepowers,lengths,and engine types all in the same class.They all went racing and enjoyed it.The more rules,the more aggro.
 
Agree with Graham, that's one very light build! My little P28 weighs just over 3000 kilos all up, with motors that are just a little heavier than BBC's, and admitedly quite heavy interior fitout, but still far from a heavy overall build.

As another guide, a Scorpion 10m cabin rib (33', twin Yanmars) weighs 4500 kilos as a std boat.

Looking at the pics you posted, one shows a view into the cabin area through the companionway, I can't help noticing that there doesn't 'appear' to be any longits, I assume the sandwich hull construction & floor are the main structures fwd? A very minimalist build. Clever fella that Jeff.
 
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