Veideo of my Lencraft 4.8m and DT55 on the water

TomKat · 07 November 2011, 22:43

Thanks to all for the advice on the outboard fitting and engine setup.

Boat is now running but not as fast as I had hoped, about 20 knots, am I right to expect more? Boat is a 4.8m rib.

Lencraft 4.8m run on River Bann in November 2011 - YouTube

I am pretty sure the engine is not revving out right due to electrical issues - oil flow and water flow not as yet connected to anything! I have ordered a tacho to fit this weekend.

Any thoughts on the sound of the revs in the mean time?

Vandad · 08 November 2011, 00:36

Quote:

Originally Posted by TomKat

am I right to expect more? Boat is a 4.8m rib.

Not really, 20 knots is fast enough for the rib with that outboard, considering you have loaded it heavilty (yourself + 2).

Try playing with Tilt/Trim and see if that helps.

thomas · 08 November 2011, 07:10

My 4.5 Valiant with a 50 4 stroke, wife, 7 year old just abut manages 30 knots with in rougher water, I'd expect a bit more but not much.

Boats&Outboards · 08 November 2011, 08:15

The engine looks like its going quite well for its age, sounds like it could kick out a bit more rpm with prop change etc but like others have said its there or There abouts.

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

TomKat · 08 November 2011, 08:29

OK, I'll update when I get the other issues sorted out, hopefully it will go a bit quicker but happy enough even at that speed as the hull seems to nicely slice through the bumpy stuff so speed at sea should be much better than I have been used to!

two stroke mick · 08 November 2011, 09:59

On my DR 490 with a 60 hp I will achieve 30 kn with a heavier load than you are hauling. I suspect that the boat is under proped

willk · 08 November 2011, 10:57

You say "about" 20 knots. Did you log this on a GPS? As you're on the Bann, you'll have to have done this both directions to get an average speed.

One helm, two wains and an auxie isn't heavily loaded in a 5m rib.

The motor looks like it could be trimmed a bit higher - did you trim up while underway until the prop "slipped" and then drop it a touch again? On water like that, that's yer sweet spot for speed.

On the subject of water - when it's that calm, and the bow has wains in it, there's nothing to kick the bow up so you could lose a knot or so...

As the lads say, a tacho will determine whether you're going to need a prop change or not.

It's a three cylinder isn't it? Have you done a compression test yet?

TomKat · 08 November 2011, 11:19

Messed about with the trim and no appreciable difference, speed measured with GPS on the phone and it felt about right i.e. roughly 25mph/20knots.

The trim thing is new to me so don't really know what I'm doing!

Compresion tests are OK, I am pretty sure its in guardian mode due to the sensors not being connected, once I figure out where to plug them in 40 knots here I come!

Will hopefully get the tacho fitted up this weekend and pul lthe prop to see what it is, have been advised on a 15" pitch being about right - it currently has a 12" dia prop fitted with an unknown pitch - why do they stamp the back of them!.

Any thoughts on the best prop?

two stroke mick · 08 November 2011, 12:10

I suspect that max speed for that rig lightly loaded is circa 30 -33 kn.

FYI if your speed was 25 mph then this equates to 22 kn

MPH *1.6 /1.8 = kn approx

willk · 08 November 2011, 12:22

Quote:

Originally Posted by TomKat

The trim thing is new to me so don't really know what I'm doing!

That motor doesn't sound like it's in limp home mode. It might be a touch under max revs, but that could be Trim/Prop/Load.

Trim and load are the free tests.

First off, I don't rate most phone GPS units. Mine often shows over 1kt at standstill - check this on yours.

Take the boat out empty and establish a base speed (take current/tide/wind into account by doing two directions and taking an average)

Then play with the trim on the motor. While under way in a straight line, at full throttle, trim out (raise the leg) in stages, listening for prop ventilation. You should hear the revs rising as you do this and I'd expect you to gain 3-5 knots. Eventually the prop will ventilate/slip and you need to drop it again to the sweet spot where you're getting max revs with no slippage. If you make tight turns in this trim, you will have instant ventilation and loss of thrust, so it's only useful for cruising/straight line racing.

The other thing I forgot to ask was have you checked the Lennie for water in the hull (is there a drain in the transom?)

Johnscubanut · 08 November 2011, 12:44

Hi there, I'd say if you increase the pitch to 15' you will definately get more speed but it will take longer to get up there? With a heavier load onboard you will find it will struggle to rev out? We used to have to drop the pitch on our dive ribs to around 13inch on our 90hp engines to allow the engines to rev out? Very heavy loads involved with us? Always trim out to the max (just short of ventilation) to achieve comfortable revs & cruising speed? I'm guessing that max revs on your engine would be around 5k?
Hope this helps & be safe but have fun out there? John

Downhilldai · 08 November 2011, 13:35

Quote:

Originally Posted by Johnscubanut

Hi there, I'd say if you increase the pitch to 15' ....

Do you know the pitch of the current prop?

TomKat · 08 November 2011, 14:08

No idea on the current pitch, tried to take it off and nut was a bit stiff so left it, will try again on Saturday. Am hoping to drop into the Suzuki guy tomorrow afternoon to get his views on the unconnected sensors, he might know what the pitch is by looking at it.

Johnscubanut · 08 November 2011, 18:15

They are usually quite tight especially if not been removed for a long time? We use a bar jammed between the blades & the gearbox & an extension socket & with a bit of careful leverage the nut should come free? We've even removed a damaged prop at sea! Someone needs to hold your legs tho? lol The stamp of the pitch size will be either on the sections between the blades or on the boss/ring where it meets with the gearbox? Removal of prop is needed to see this! i.e 12 & 1/4 x 15 (Diameter x pitch) Hope this helps?

TomKat · 08 November 2011, 22:06

good tip John - thanks!

Johnscubanut · 09 November 2011, 16:38

Your most welcome!

TomKat · 09 November 2011, 18:25

Checked the prop, it is 11.75 x 12, am I right in thinking that this is on the small side pitch wise and the engine should be revving out above 5500rpm at WOT?

I will fit a tacho this week to verify rpms on the water (hopefully this weekend weather permitting!)

Boats&Outboards · 09 November 2011, 18:59

I think your currently revving at around 3,400 looking at the video. Not sure what its limit is off hand but if your right you've plenty of room to play with the prop

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

TomKat · 09 November 2011, 19:26

Thanks Peter

This is all new to me so bear with me, would an 11.75" pitch (the one on the boat) be realtively easy to turn thus allowing the engine to rev out higher that recomended WOT? i.e. if I put a 15" pitch prop on as has been suggested would this increase or decrease the WOT revs? If my logic is correct this should decrease the revs?

Cheers again

Poly · 09 November 2011, 20:04

TomKat,

The engine shouldn't be in guardian/limp-home mode because the gauges aren't connected.

I'd be surprised if you could get 20-22 knots in limp home mode.

Quote:

I think your currently revving at around 3,400 looking at the video.

not doing >20 knots with an 11.75" pitch prop.