How many knots off top end does this equal

oGaryo

oGaryo

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Hi, we're in the final stages of purchasing a Sealine S28 and one of the little niggles I have is she only pulled 25knts in a slight sea state with a garden hanging off the back of the boat on a WOT run I held prior to the main survey and seatrial.

During the final survey, the sea state was too rough to conduct the WOT tests so I am left not knowing how she'd truely perform with a clean bum.

These two shots show the extent of the growth within an 8 month period as she was lifted and had significant work to the drives in March of this year. The other thing to mention is the aft props on both drives are not perfect so that will affect performance too, surface corrosion on one and a ding to the other.

All things considered then, garden and barnacle growth cleared from the drives, trim tabs etc, bum scrubbed of the light fouling and aft props sorted, am I likely to hit the 32knts she is reported as being able to reach with her engine and drive setup (KAD 32's fitted)?

Thanks in advance for your opinions.

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cheers Gary
 
well.... have said this before but when we had the last rib, (45 Kts WOT when clean) we left it in the water for 6 months or so, and at WOT we were just about getting 35 Kts in very similar conditions. when the boat was lifted it was dirty but no way near as bad as that!

Im not suggeting you are going to get 10 kts extra when clean but its surprising how much speed you can loose.

I understand fouling on the leg is a big speed sapper as well and you have that and some!!!

will buy you a pint if you cant make it up past 30 Kts when you are clean and in the right conditions!
 
REally difficult to say Gary. With your hull pic, I can't see much growth. Clearly there is a lot arond the drive, but not much of this would be in clean water flow at 25k+, so really hard to predict the impact.

Can you offer so much, with the balance to be paid should she meet the target speed? Is the current owner claiming 32k or is this the Sealine blurb?

A friend of ours really only gets 25k out of his S28 in the Brizzle Channel, with the KAD32's.
 
I'd say that fouling could easily account for 5-7 kts. The props and hub have quite a few tubeworms on them, and the hull seems to have a layer of slime, which will look a bit like a carpet when in the water. I was 8 kts down in the Windy with no more fouling than that.
 
I have always been slightly suspicious of the claimed 32 knot top end on the S28 with KAD32's.

We have the S23 with a single KAD32 and it is good for 30 knots even with slight fouling (not the water garden you have there:D) and slightly dinged props.

The S28 weighs more than twice as much as the S23 yet only has twice the engine power so how can it be quicker?
 
My experience has been that the fouling on the props and hubs will be a real killer, as Nick says.

btw, I quite like the wheels: is this one of the new amphibious S28s? :D
 
CX54WEK said:
I have always been slightly suspicious of the claimed 32 knot top end on the S28 with KAD32's.

We have the S23 with a single KAD32 and it is good for 30 knots even with slight fouling (not the water garden you have there:D) and slightly dinged props.

The S28 weighs more than twice as much as the S23 yet only has twice the engine power so how can it be quicker?
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I'll try to answer that one with a video, not just for the top speed element of the S28 but also for the entertainment value of the lady on board half way through the video:D They seem a lovely couple.



At a guess, weight on land between the two boats may be double but when skipping along the surface, that difference is probably lessened
 
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thanks for everyones replies, that gives me confidence I'll see a marked improvement once I've had a proper fettle with the setup... assuming I buy the boat of course
 
For What It's Worth........

My opinion is that, apart from scrubbing off the speed, that amount of undergrowth would/should show on the tachos, you won't be able to pull max revs, the boat will feel like driving through treacle.

Example, One Away had bad fouling, she would only pull 2900 rpm 25/27kts after a visit to sealift2 in the Medina and a scrub & wash off we came back pulling the full 3900 rpm 36kts, felt like a different boat.:eek:
 
epervier said:
My opinion is that, apart from scrubbing off the speed, that amount of undergrowth would/should show on the tachos, you won't be able to pull max revs, the boat will feel like driving through treacle.

Example, One Away had bad fouling, she would only pull 2900 rpm 25/27kts after a visit to sealift2 in the Medina and a scrub & wash off we came back pulling the full 3900 rpm 36kts, felt like a different boat.:eek:
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cheers Dave, hope you've an Loreen's been keeping well by the way mate... She was down a bit on revs at 3500 (both engines).. should be nearer 3900 apparently
 
I wouldn't proceed Gary unless the boat actually gets to 3900 revs and the quoted top speed. Otherwise you could be searching for extra knots despite the clean bum/props and anything to do with green engines cost lots of money....I can vouch for this as I've lost 5 knots with a clean bum and it's costing me dearly. Wait until it's performance is proven rather than take a punt....
 
CX54WEK said:
I have always been slightly suspicious of the claimed 32 knot top end on the S28 with KAD32's.

We have the S23 with a single KAD32 and it is good for 30 knots even with slight fouling (not the water garden you have there:D) and slightly dinged props.

The S28 weighs more than twice as much as the S23 yet only has twice the engine power so how can it be quicker?
Click to expand...

I have no idea, other than it is able to run with bigger props, A6 is the standard fitment. 34kts is the rated top speed for A6's on that drive, and 34kts is definitely possible with half fuel on board, and clean hull/props. Using C5 stainless is rumoured to hit 35kts, but this could be folklore.
 
crazy4557 said:
I wouldn't proceed Gary unless the boat actually gets to 3900 revs and the quoted top speed. Otherwise you could be searching for extra knots despite the clean bum/props and anything to do with green engines cost lots of money....I can vouch for this as I've lost 5 knots with a clean bum and it's costing me dearly. Wait until it's performance is proven rather than take a punt....
Click to expand...

Yep, despite my earlier comments that I think it's probably just due to fouling, i'd always want to see a boat run at full speed before buying it. Is the S28 still in the water? If so, it shouldn't take long to wizz out again on a calmer day, and you could offer to pay for fuel to show the seller you're genuine.
 
I'm bound to say I can never understand why a vendor would offer a boat for sale with that much muck underneath. It will only throw up questions like this and ultimately I suspect they will have to get it cleaned off.

I would have thought the growth would result in lower revs. Damaged or dirty props could potentially result in higher revs for a given speed as they are not gripping the water properly.

What I would say is that if the engines were going to smoke they would do it on. Dirty hull, so if they were clean with **** on the bottom they won't get any worse with a clean underside.

Henry :)
 
I was surprised at the level of growth on a great many boats in Brighton Marina. It looks likes it a big problem there, perhaps a berth holder on here will confirm ?
 
I,ll add my two Penrth
Looking at the pics it's the parts below the exhaust bit that really need to be clean .Especially the props and spinner these need to be real shiny to get near WOT and the claimed max speed - unless the prop pitch is overly low.
Our boat is lifted ( like many) arround Easter antifouled etc ,and engines KAMD 300's serviced by VP agent
Part of this is a written WOT at which RPM and how fast on the GPS - a kinda post op sea trial ?
This appears on the invoice from the VP technician., so I have a refference point
Typically I turn up 2 days later and " test" out the numbers .
Yup - correct 3700 rpm= 39 knots.
( .Bills are settled when I return home)- everyone's happy
However as the season progresses the numbers head south
Due to fouling - even 6 weeks Interval in the peak summer months and wot struggles to go over2500 rpm
However legs up ,arm down over the swim platform clean scub props and whey-hay 3400-3500 rpm maybe 34 -35 knots , then while swimming cleaning the main submerged leg perhaps 1 knot more
So you can see the diff between -" real world " WOT/ max speed and 2 days after a fettle .
I normally do 3000 RPM @ 28-29 knots in April - this drops to 26-27 say by late August - but I can ease up to 3100 to achieve 28-29 cruise and do late in season
The Hull seems to develop a slime layer to touch as the season progresses , so some more Knots lost.
Props need to be as clean as poss to get any where near claimed WOT/ max speed .
So you will get a few more knots after a fettle ,but WOT and sustained ( reasnable econonical) cruise are two different things .
.
 
crazy4557 said:
I wouldn't proceed Gary unless the boat actually gets to 3900 revs and the quoted top speed. Otherwise you could be searching for extra knots despite the clean bum/props and anything to do with green engines cost lots of money....I can vouch for this as I've lost 5 knots with a clean bum and it's costing me dearly. Wait until it's performance is proven rather than take a punt....
Click to expand...

+ 1

Why take a gamble? Get out there again when conditions are favourable and give it some welly. If performance is still down then you know the boat has a problem and can haggle or walk away. If performance has improved then you can go ahead and complete the purchase without worrying, assuming everything else is OK.

If there is any resistance to a second sea trial then offer to pay for the fuel. If the owner still says no then walk away.
 
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