Shaft length issue

Courageous · 07 May 2011, 12:02

Hi chaps,

well my boat went out for sea trials yesterday. She's not fully prepared yet but I had to get her off the drive and in the water at the back of my house. The issue is this:

I bought the boat with a kankered Mariner XL and by mistake bought a replacement Merc L shaft. I didn't even know that XL existed until I noticed the position of the anti cavitation plate on the new rig. Checked on Valiant site and yes there in Black and White was the statement - 1 Motor = XL, 2 motors = L.

I have spoken with a few people who thought I might just get away with it but under trial yesterday it was all too obvious to me that the motor was too ready to over-speed with a resultant loss in boat speed. I found I was able to judicially get her up to speed with slow lever movements but there came a point where she lost grip and the motor went for it! I got about 17 knots in a slight swell.

I have considered swapping legs and even got as far as removing all of the powerhead nuts but couldn't get the powerhead off the original motor. She had been sat in the water unused since she blew up in 2008! I have it in mind to continue trying to remove that leg, refurb it and place that on the replacement engine but that will be a winter project now. The boat HAD to go in the water so that we could give something to the guys coming on diving holidays here.

Now, thoughts appreciated from you guys. Does anyone think this setup might benefit in any way by fitting doel planing fins at all or would that be a total waste of time and money?

The boat's a valiant dr750, engine now 150hp merc, long shaft and have laser 17 prop fitted (stainless steel).

Would very much appreciate any assistance here.

Thanx in advance - Ian

Kernow Buoy · 07 May 2011, 12:28

Ian I won't comment on the doel fins (cause i don't know) but may be worth questioning whether a 4 blade prop would help, more grip once planning apparently.

martini · 07 May 2011, 12:48

Sounds to me like it's well too high and nothing other than lowering the prop in the water is going to sort it. Doel fins will be a waste of time, a 4 or 5 blade prop may help but it's still going to be in full race mode ie rooster tail out the back, no grip, bad handling etc.

If it's just a couple of seized bolts standing in your way then persevere or get an expert to have a go.They'll come out one way or another. ( Just please please don't start another seized bolt removal thread

)

Nos4r2 · 07 May 2011, 12:53

How about a jackplate? The setback might compensate for it being too high.

Courageous · 07 May 2011, 13:00

Hehe! No, no seized bolt threads from me

Sounds like a pun anyhow!

I'll invert it sometime and drop some good releasing agent down there. It'll come in time I expect. Now that she's in the oggin' leg replacement is going to be a costly measure. It costs 80 euro for a lift out, same for a lift back in. Then there's the time element. Was hoping beyond all hope for an alternative but even the four bladed props are fairly expensive aren't they? If XL leg or 4 blade props are my only choices I'll have to consider them of course.

The cavitation plate's around 5 inches above the base of the keel. Obviously the XL would be right at the keel level on this basis.

There's an ad on ebay for 2 16 year old XL merc 200's. They are up for 4 grand sterling for the pair. They are one normal and one contra obviously once paired on a RIB. I made an offer but it was refused outright. They are in Alicante (about 7 hours drive from me). I was thinking one on the boat and one spare in case the first got destroyed by my punters. Can't justify 4k even if they DO only have about 20 hrs on them as stated! They're still 16 years old!

Hmm.......

Courageous · 07 May 2011, 13:01

Sorry NOS, was triping when ya posted.... What's a jackplate?

Ok I see now..... Bit ugly eh?

blufin · 07 May 2011, 13:56

If you can drop the box off the L motor and not the XL motor Bay Manufacturing in the US do an extension kit to turn your L to XL. Might get you going a bit quicker. iirc about €600. Welcome

Cheers
Gerry

Nos4r2 · 07 May 2011, 16:27

Quote:

Originally Posted by Courageous

Sorry NOS, was triping when ya posted.... What's a jackplate?

Ok I see now..... Bit ugly eh?

Yes, not pretty-but a decent adjustable one would also allow you to 'tune' the motor height nicely.

Prime 2 · 08 May 2011, 16:51

Quote:

Originally Posted by Nos4r2

Yes, not pretty-but a decent adjustable one would also allow you to 'tune' the motor height nicely.

Hi Had the same problem on one our Hydrosport. The boat was rigged with a standard and not an XL.

I had a CMC jack plate fitted and also a new prop with a slightly bigger pitch,

This made a huge difference and has cured the problem. I now only get cavitation in a tight turn.

I can get some pictures when I am at the yard later this week.

Cheers

Keith

Courageous · 08 May 2011, 19:00

Hmm bigger pitch? I have a 19 but am running a 17. Could this make a difference guys do you think? OR did the jackplate make the bigger difference in Keith's case?

Nos4r2 · 08 May 2011, 20:02

Quote:

Originally Posted by Courageous

Hmm bigger pitch? I have a 19 but am running a 17. Could this make a difference guys do you think? OR did the jackplate make the bigger difference in Keith's case?

It'll be the jackplate.

bosun · 08 May 2011, 22:27

I suppose cutting out the top three inches of the transom and glassing it over and then dropping the engine down will put the powerhead too close to the water?
I've got the reverse problem with a new humber 4m,the boat is built for a long shaft motor (apparently) but the longshaft 30 honda that I fitted (was on an SR4) ended up with the cavitation plate three inches below the bottom of the transom,and ran BAD,so I raised it up to normal height and its ok but looks odd. I need to speak to humber and measure the honda first.

Courageous · 05 July 2011, 11:26

Ok it's update time: Changed 17inch prop for 19inch and found a definite improvement but not enough. Bought a Whale Tail planing fin off the bay of fleas and fitted that today and the sea trial showed a vast improvement with us up to 26 knots at 6k RPM on a flat seas. The engine behaves much better than before as it seems to have stopped ventilating after passing over a wave top which was most disconcerting. We simulated this condition as best we could using other boat's wake. There's no doubt that we're not going to win any competitions especially on the economy front but I'm happier than before. We get the impression that we could cope with a higher pitched prop so if anyone has a stainless unit for a merc 150 greater than 19inch then I have a good home for it

Thanx again for all your advice so far. We're still on the lookout for an XL engine as the long term solution.