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Old 05 June 2014, 07:38   #1
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Country: UK - England
Town: Eastbourne
Boat name: Velassaru
Make: Lomac
Length: 8m +
Engine: 2 Verado 200hp
MMSI: 235102197
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Posts: 21
best Verado props - speed?

Hi I'm just finishing getting my boat tuned since it came out of the water for the first time since we bought it (one year ago). It is unbelieveable how much was wrong, but anyway having serviced my 2 x 200hp Verado's, fixed a sticky valve, replaced spark plugs I got top speed up from 33 knots to 46.4 knots already @ 6000rpm

That all with the engines too low by two holes (2 inches)!!

So today they go back on - at the right height. Now the boat shop says (and Mercury UK says) I am probably under-propped and may well be redlining my engines at full speed/WOT and cavitating on acceleration. So chances are I need higher-geared props. It looked easy at first but suddenly I discovered Mercury Racing and their choice of 10 or more propellors, depending on boat type, natural bow lift, weight, whether you target top speed or efficiency etc.

My boat is 8 metres GRP rib, 300l fuel 70l water, probably 2 tons with engines? I don't know what "natural bow lift" is but my optimal trim used to be just shy of 10 degrees. I don't want to compromise top speed but I spend my time cruising at 4,000 in good weather (33 at the moment) and I think 3,000 / 22 knots or so once a breeze and chop comes into play, maybe the other 1/2 of the time we are out.

So do I get a Bravo 1 Verado, or a Cleaver style, can I get Lab Finish (low bow lift) or do I need Pro Finish (has more bow lift), is my boat light or "heavy", 3 blades or 4, Pro-Max in X7 steel looks to be nice. Any advice very welcome please? The exact pitch I will just base off of what I already have (unknown to me yet)

Of course I will do a sea trial this weekend if possible to find all my new RPM / Speed / Trim / lph / Range data with my newly correctly positioned existing props first. I secretly sort of hope the engines run out of revs right on 6,250 or 6,300 - just before the props run out of gearing - and then I can change nothing and would I have a 56mph boat! No complaining there. But 50 knots just sounds cool
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Old 05 June 2014, 10:17   #2
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Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider Boats
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Engine: Tohatsu 18 /30 HP
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Did you achieved notorious water splash at back transom or high wake before 2 holes down position was raised. What's your current wot rpm on a flat calm no wind water course with engines sitting at new higher position ?

Happy Boating
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Old 05 June 2014, 11:45   #3
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Country: UK - England
Town: Eastbourne
Boat name: Velassaru
Make: Lomac
Length: 8m +
Engine: 2 Verado 200hp
MMSI: 235102197
Join Date: Jul 2013
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before in lower holes I had backwash up the transom such that water jetted up the deck drains the wrong way and half floods the cockpit, so I have to shut the seacocks. Mechanic says transom vertical should be clean on the plane with these. no upwards spray tho. wash is quite big but I never had anything to compare it to yet

hoping flat water tom or Sun to trial :-))
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Old 05 June 2014, 11:46   #4
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Country: UK - England
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Boat name: Velassaru
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Length: 8m +
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oh current (old) WOT rpm on flat water best trim is 6,000 rpm plus change, 46.4kts (GPS, one direction)
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Old 05 June 2014, 16:41   #5
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I'd wait for another test before deciding on props. You will likely gain some rpm, but as to how much (from reduced drag off the lower units) I doubt anyone can guess.

jky
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Old 05 June 2014, 16:58   #6
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Country: UK - England
Town: Poole
Boat name: Half Cut
Make: Cobra 8.6
Length: 8m +
Engine: Verado 275
MMSI: 235104619
Join Date: Jun 2011
Posts: 378
Before trying race props have go with Rev 4 or the new Enertia Eco. Big props, lots of blade area very good grip and can be mounted high. The rev 4 is stern lifting, so planes very easily, (I can plane at 10 knots @2500 rpm) the Enertia Eco (not the same as Enertia) has a bit more bow lift, but claims very good (+20%) economy at cruise. You might lose a little top speed, but better cruise and handling. Try asking on the PropGods forum. Good luck it's a dark art, not a science!
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Old 05 June 2014, 17:58   #7
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Country: UK - England
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Anyone tried a rev 4 with a stepped hull?
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Old 06 June 2014, 03:57   #8
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Country: UK - England
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I haven't but many have on big CCs in the States. Try a search on The Hull Truth forum.
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Old 06 June 2014, 04:09   #9
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Country: UK - Channel Islands
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I think a 2 ton boat with big twins is going to need lots of stern lift and plenty of grip on acceleration, I'd be looking at rev4's first.
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Old 10 June 2014, 11:58   #10
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Country: UK - England
Town: Eastbourne
Boat name: Velassaru
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OK, engines raised, grp all fixed too, the shop did a sea-trial and told me the following;

1) much less spray/wake and clean transom, felt lighter/cleaner
2) no water spouting backwards up the drain holes from the deck
3) got up to about 40mph (sea was not flat)
4) no cavitition issues (was a potential worry), gripped well in a hard turn
5) rides level, no longer required the single fixed trim tab on starboard side
6) On the way back in the right engine suddenly lost power as if the rev limiter is coming in at about 2,000 rpm (like in neutral - so as if it doesn't recognise it is actually in gear). Phil mechanic reckons there is a switch deciding this that has failed.

I took her out Sunday and opening up really gently no redline limiter hit at 1,000 or 2,000 or 3,000, so I kept on going. In 20cm of long swell (i.e. almost flat), 2/3 of a tank (200l) and 3 adults, I managed WOT for a bit. Peak speed on the GPS was 46.7 or 46.9 knots - but not steady. "Only" 5,900 rpm I say only it is at least 100 maybe 200 less than I had achieved with the engines in the "wrong" place, but that was on a glassy millpond. I did not have time to really refine the trim to the very last degree, I think see a small improvement on my old record of 46.4 but I was hoping to see more. I have no idea the slowing effect of a very gentle small swell but the boat is still moving up and down as well as along so maybe a knot or two of drag? Anyway it is already pleasing I can now leave sea-cocks open without flooding, remove the asymmetric fixed trim tab "gaffer tape" fix that was on before, and knowing it is set up how it should be. I hope to see more efficiency slower (WOT was 180lph+).

So not a full sea trial - but great fun, and we caught cod (first ever) and pollack (also first ever) and smaller spotted dogfish. So Sunday night at 11 we were filleting fish with how-to by youtube on the iPad, kitchen looked like the fishmongers by the end of it!

I did manage, when accelerating hard, to replicate the power loss, once, but after a throttle all the way back and then gentle increase and it worked again. So I am limiting myself to a very few miles until such time as cause is identified and rectified, then back to Brighton, Rye and so on. Bring on next weekend! I think changing propellor will now actualyl wait until I have the perfect flat water to max her out and really verify top speed at best trim and at various other rpm to see what need there is, it could easily be the ones I have are perfect...
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