Trim / Chine walking / Engine height

Daniel · 18 December 2003, 17:36

I have found that top-banana gives a very wet ride unless i trim the engine out a fair bit, i think this is because trim "0" is infact less than vertical and i am diging the bow in too much. The trim gauge runs between "0" and "10" at which point you lift off the top of the rams and into trailer position. I am finding "2" gives a lot drier ride...

...however, when trimed out i find there is a tendancy to 'chine walk' and feel a little unstable - to avoid this i seam to have to get very wet by trimming in.

My questions are this:

1) Any comments at-all
2) Is this linked to the height of my outboard on the transom?
3) Any people got an idea at what level of trim they normally 'use' in a moderate following sea trying to maintain, say, 30 knts.

The Jackeens · 18 December 2003, 17:57

Jwalkers comments I found very useful

http://rib.net/forum/showthread.php?...s&pagenumber=6

Might help

and a VERY GOOD THREAD

paul

Daniel · 18 December 2003, 18:14

Thanks paul

Quote:

Originally posted by jwalker
Anything which helps to keep the engine under control will be good. Very tight steering with as little as possible free play will help

This could be what it is, i've still got a little air in the steering, and i'd forgotten about it

Watch this space.

seatreks · 18 December 2003, 18:23

Used to have a Osprey viper 7.2m with an 165hp yamaha inboard diesel, great boat & it provided many days of fun but it is simply a wet ride, not as wet as the deltas!!, but still wet, changed it for a 8.4m red bay, lost the fun factor but at least I am staying dry.

Good luck with the Osprey.

Rogue Wave · 18 December 2003, 18:53

Sea Treks what speed did you get from the Viper please. I have a 165 Yamahs and am thinking about an Osprey Hull.

Cheers
Stuart

Pete7 · 18 December 2003, 19:43

Daniel,

I used to have a 5.95m Osprey viper with a Yam 115. The only modification I had the builder make was to move the console and 30 Gal tank back 10" to give a central position to drive from. The boat had superb handling and I have yet to find another rib which provided such confidence to all those who drove her. she deffinately wasn't a wet ride and would confidentally drive the nose into the back of a wave knowing she would ride up the wave and over the top.

How much weight have you got up the front in the anchor locker ?
also what sort of speed are you experiencing chine walk ?

Sounds like you might need a little weight in the back end, try a couple of friends. as you suggest it could also be caused by the height of the engine. Easy enough to raise and lower it until you find the best position. Is the engine on the centre line ?

Pete

Daniel · 18 December 2003, 20:05

Thanks for the ideas Pete, in order of the points you have raised:

confidentally drive the nose into the back of a wave knowing she would ride up the wave and over the top.

I have the same confidence - thats one of the things i love so much about the osprey, it just keeps inspiring more and more confidence infact...it's just i'm getting wet!

How much weight have you got up the front in the anchor locker ?

Quite a lot - large anchor and chain etc.
Not that much in the rear, but 200Kg of engine, which i beleive is on the limit for the 6m osprey.

also what sort of speed are you experiencing chine walk ?

I'm not sure it is a classic case of chine walking, but similar. I'm yet to experience it on the flat, but i would say in a moderate following sea i can feel it at 35knts +

Sounds like you might need a little weight in the back end, try a couple of friends.

Yes, console and 220li fuel tank are quite far forward. Trouble finding friends to come out this time of year. I need sunshine and a flat day to diagnose further i feel.

as you suggest it could also be caused by the height of the engine. Easy enough to raise and lower it until you find the best position. Is the engine on the centre line ?

Engine is offset quite a lot, couple of inches. Never had hyd. steering before so not used to not 'knowing' what speed engine is neutral at.

I do feel the air causing a little play in the steering might be a big factor. I'll pull her out this weekend and sort that - i've a few more finishing touches to do anyway.

DM · 18 December 2003, 20:11

Dan, why don't you ring Mr. Osprey himself. Gary Mirley 01902 606777. I am sure he will be able to advise you on set-up.

DM

jwalker · 18 December 2003, 20:40

Chine walking at 35knots is a serious handling problem. Presuming the hull design, rigging etc. to be sound it is more likely to happen when there is not much hull left in the water. In fact, trimming the bow down a tad will increase the water line length and can often settle the boat. Going fast with too much load in the stern can induce it. Although it doesn't follow your description but, particularly since you say the boat is heavy in the bow, are you sure it's not steering by the bow? This is worse in a following sea. The boat does not rock from side to side, it tends to veer off course and needs to be corrected quickly but it can then veer off to the opposite side. Slowing down calms it. Just a thought.

2" offset is a lot too for a 6mtr boat. Your thrust line is way to the side.

I would expect a boat to be able to cruise 'hands off' at about 35 - 40knots in good sea conditions.

As for the boat being wet; doesn't the Viper have limited overhang of the tubes over the hull? Nothing to deflect the water downwards?

seatreks · 18 December 2003, 21:58

Hi Rogue wave, we managed to get an average of 40knts, I was very happy with the old girl and can confirm she never chime walked with me, but as the years creep on you need a bit of comfort, have just ordered an 11m (twin yam 270hp) Redbay Stormforce with seating for 12 and sleeping for 2, had considered 2 x Yanmar 300hp but had a bad time with the bravo 3x drive, we hope to touch 40 knts with the new boat. Cheers

Pete7 · 18 December 2003, 22:02

Daniel is the fuel tank full ? 220 l is a huge amount of petrol that weighs about the same as the engine. I think she is trimmed down by the bow as JW suggests which is were the water is coming from. Never had this problem unless very strong wind blew spray off the wave. this pic is deffinately to far down.

Pete7 · 18 December 2003, 22:03

this one is better,

Daniel · 18 December 2003, 22:08

I don't think those pics are fair for a number of reasons:

1) i think the first pic is infact the 'landing' after the second pic
2) they were taken during runing-in when i was not supposed to adjust the trim, so it was "0" which to me looks like under trim if you get what i mean.

---EDIT---I'm wrong, having just checked the filenames they were taken in that order.

I agree 220li is a lot, and yes it is full (or was). I still think the air in the steering might just be the ticket though.

DM - When i called Osprey a few months ago to pick their brains i did not find them as helpful as you had suggested i might, i suspect i might have spoken to a gimp though, will try your contact, cheers. When you coming down to sample my new toy?

Pete7 · 18 December 2003, 22:09

You have a planning wedge on the Osprey which helps a heavy dive boat get onto the plane. At very high speeds this will affect the handling but not 35 knots, she should be hands off at that speed, instead you are bow steering. Loose the anchor and some fuel.

Bit worried about that much offset, still nothing that can't be sorted with a little trial and error.

Have you measured her with a tape measure, worth a thought

Just using your pics as examples, top one shows too much hull in the water.

Pete

Daniel · 18 December 2003, 22:12

Another pic.

Daniel · 18 December 2003, 22:12

And another, looks OK here

Daniel · 18 December 2003, 22:15

Another, look at the spray???

As for offset i must confess i have not measured it, we took an executive decision to use to exsisting holes and correct it later if we had to. Unfortunatly i don't know what engine was on her origionaly, DM thinks it might have been a 200. It might only be 1". Will measure!

Daniel · 18 December 2003, 22:18

Somewhat off the subject, but i just spotted this photo. It's a constant struggle to keep the bow IN on my friends boat

Pete7 · 18 December 2003, 22:32

Daniel, sorry I meant measure her end to end.

Spray looks fine, not coming in the boat. You had a BWM last with concave hull shape at the front which directed the spray right down into the water. the osprey has a much more roundedbow which gives the reserve of bouyancy and stops her stuffing.

Still nice boat and her fit out looks superb.

Pete

jwalker · 18 December 2003, 22:39

Daniel, it doesn't look bow down but it does look heavy. The hull's not full of water, is it? Trimming out, as you mentioned, would send the water to the stern and make that end seriously heavy. Opening the throttle wide might then induce a chine walk once up to speed. Just guessing.
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Just looked back at your pics. 4 folk on board, 3cwt of fuel plus your anchor and, no doubt, other equipment. You're not expecting too much from a hull about 5mtrs long. are you?

Your pal's boat is just one up. Not a good comparison.