Power upgrade...how much is too much?

Greenheart

Greenheart

Well-Known Member
Joined
29 Dec 2010
Messages
10,384
Visit site
I know sails, I know nothing about engines afloat.

But I always admired those super-sleek 1980s Sunseekers. I still think the newer designs are an ugly evolution, even if they're better technically.

318681-sunseeker-portofino-xps-34520426_thb.jpg


I sometimes look at the thirty-year-old XPS/Portofino models and am usually surprised to find that these boats aren't (and never were) as fast as they looked.

Presumably that was a result of prudent, economy-minded engine choices...

...these were described as deep-vee race-bred hulls, which I'm supposing could handle lots more power than the average customer wanted to pay to run.

If the XPS34 had a pair of 200hp engines, it was probably good for 25 knots...

...but how much power is the hull good for, if the owner's wallet could stand the strain? Were any of these boats fitted with as much power as they could handle?

Would petrol be a better bet than diesel, costs aside? And how much speed might she achieve safely, given upgraded props, etc?

Thanks in advance. :encouragement:
 
Last edited:
Twin 230hp diesels on an XPS34 - more like 35kts+ ?

I've seen the same boat fitted with Merc 7.4L V8 454's (375 bhp per side).
No idea how quickly your wallet would empty with those :)

.
 
Last edited:
FlowerPower said:
I've seen the same boat fitted with Merc 7.4L V8's (375 bhp per side). No idea how quickly your wallet would empty with those :)
Click to expand...

Thanks...but any idea how quickly those engines would get you to the bank, to refuel your wallet?

Are those big Merc petrols lighter than the much smaller diesels? (Sorry, I've really no idea, just interested.)
 
Thanks FlowerPower, useful link there. Great looking boat and a bargain, apparently...doubtless a shocker to run, but I was mostly interested in potential performance. :encouragement:
 
Last edited:
I think Don Shead at the time 80 s we are talking about here did design some v good performance hulls .
Thing is the engines 200 Hp (or what ever) were what they had to play with back then .
The point is this - not mentioned ^^^ regardless of the ultimate headline top speed WOT etc ,it’s the everyday running speed .
A deeper V high deadrise hull like the Porto XPS 35 mentioned will be able to keep a fair turn of speed in every day chop - while competitors have to back off .
So the Sunseeker ploughs on comfortably at say 28 knots in 2 M short chops while AN OTHER , flat dearised same L backs off to say 22 knots - still planning .
Any faster the competitors just slam the occupants into submission.
How ever on a pancake flat sea , indeed the “ competitors “ may be a few knots faster for that magazine headlines grabbing line .

Through the 90,s early noughties folks ie the buyers wanted more luxury, so the boats got Beamer , Ok Volvo Penta had a mini arms race re Hp , but Sskrs sub 45 ft just got Lardy .
Extra Beam means usually a shallower deadrise , flatter aft sections mean more lift , so the builder can pack more Kg - think luxury in .
We started on a Portofino 35 circa 2003. Twin KAD 300 ,s about 9000 Kg , inc geny , Aircon , + much more performance blunting though back then considered essential stuff .
It looked like a Sunseeker , was named a Sunseeker , see the pic .
But did it go like a Sunseeker of the 80,s ——- I,ll let you make your own conclusions .
Hint - if it did I would have kept it or got another

https://imgur.com/gallery/6kHzz
 
I am not sure there is a proper answer to the OP’s original question. I think he is asking why a boat like the one pictured didn’t go faster than what is in today’s terms a relatively normal top speed, and secondarily, if you went at it money no object how fast could it go ?

Therefore on the one hand, engines in those days were heavier and less efficient. Outdrive legs were fairly unreliable with higher HP engines, especially with higher torque Diesel engines. In fact I can’t remember what the largest Diesel engine outdrive combo was, but I’d be surprised if it was any bigger than 250hp. Petrol engines would have been more acceptable in terms of power to weight and outdrive power but probably not much more ....maybe 300 or 350 hp but everyone hated Petrol engines back then because a) they caught fire and blew up, and b) because Petrol in boats cost about 5x the price of marine diesel (ah those days.......) when marine fuel was taxed very differently.

The hull however would have been able to handle higher speeds. don Shead designed boats for racing and these hulls would have been good for 50 or possible even 60 knots if you tried hard enough........ reduced weight, increased power, balanced and trimmed the boat correctly, props selected only for top speed etc etc.

So then, the question is how fast would the Boat go if you approached it today money no object. Well you may find that the engine bay only has room for a certain amount of Diesel HP, and unless you were prepared to go really mad and change the drive options, say to surface drives, then you would still be limited to what Diesel hp (high torque) you could put through the outdrive. Petrols on the other hand are smaller and you could probably go crazy in terms of what HP you could get into the engine room and still stick with outdrive, a pair of mercruiser racing 660hp (each) supercharged Petrol engines running through NXT drives........ you’d get more than 50 knots I reckon...... probably 60 ish......but I don’t think it would be much fun nor very comfortable except on dead flat water.
 
At 55kts in a boat that old, I would be worried that an engine might be about to join me in the cockpit at any time.
 
FlowerPower said:
At 55kts in a boat that old, I would be worried that an engine might be about to join me in the cockpit at any time.
Click to expand...

Ha ha. And with good reason. I think the point of the money no object bit would be to make sure it was all up to standard. Otherwise it’s would just be Wile E Coyote strapping an engine from a 747 or even better, some sort of massive solid fuel rocket , onto the sun bed and then lighting the touchpaper !
 
It would also be sensible to point out to the OP that if he gets a Boat that does 50 knots or more, his wife will hate it, and probably him !

This effect can actually begin much lower down on the speed scale as well, but is almost guaranteed above 35 knots.
 
Portofino 31 does just over 30 knots with 2 AD41's if I remember correctly. My first big boat, always brought me home safe.
 
Boatbore said:
I am not sure there is a proper answer to the OP’s original question. I think he is asking why a boat like the one pictured didn’t go faster than what is in today’s terms a relatively normal top speed, and secondly, if you went at it money no object, how fast could it go?
Click to expand...

Lots of intelligent answers here, thank you gentlemen. It may be essentially a stupid question, especially if no 30-year-old hull is likely to be up to the arduous job of being pressed harder than she was engineered to when new. As a sailing man, I hadn't thought of that. Actually, my motor-time has been limited to a club RIB, and I detested the slamming in what were moderate conditions.

My subjective view is that the mid-80s Sunseekers achieved a summit of sexiness, so I based the question on them. But perhaps I ought to ask which newer boats were built for high speed and acceptable ride in waves, rather than luxury-carrying ability. I wonder if anybody is building really fast boats which could be cruised, and stressing the performance rather than the accommodation?

I'm always amazed by the excrescent wings and hideous logos which adorn race-boats, but I guess it's only styling, which can be changed. I'd like the boating equivalent of a BMW M5 - hugely fast, without a lot of uncouth fins, stripes, stickers and pipes...

...p'raps I'll end up shoehorning a futon and portaloo under the foredeck of a discreetly painted Cigarette. :rolleyes:

5123835_20150612112147580_1_XLARGE.jpg
 
dancrane said:
I wonder if anybody is building really fast boats which could be cruised, and stressing the performance rather than the accommodation?
Click to expand...

I’ve seen pictures of a bed, a fridge, and a loo squeezed into the nose of various Bladerunner boats, if that counts?

Pete
 
dancrane said:
I ought to ask which newer boats were built for high speed and acceptable ride in waves, rather than luxury-carrying ability. I wonder if anybody is building really fast boats which could be cruised, and stressing the performance rather than the accommodation?


View attachment 68420
Click to expand...

Well I fact quite a few Italian yards have “ stressed performance “ and most have combined luxury too .
Obviously I,am biased but my wife “ detests Slamming “ too .
Others are Otam , Baia , and Magum ( American I think ? )
Once again it’s down to the deadrise our boat is 23 degrees at the transom .Oh and a couple of big engines too .
 
Last edited:
dancrane said:
I wonder if anybody is building really fast boats which could be cruised, and stressing the performance rather than the accommodation?
Click to expand...

Searay Pachanga? Available in 22', 27' & 32' models. Could be cruised and pretty quick generally. A big block Pachanga 22 (below) will do near 60mph as standard I believe.

Pachanga22.jpg

This YouTuber claims 89mph from his modified (600bhp) Pachanga: https://www.youtube.com/watch?v=S8ldvpQ3FeU
 
You must log in or register to reply here.

Share this page

Top