New Rib is giving me sleepless nights

simsy · 18 December 2012, 11:35

Well not that concerned really, but please comment on my issue...

My new 2010, oceanrunner 4.1m rib has a 30hp tohatsu efi 4 stroke. power trim etc..

All looking as new, done very low hours clearly...

The motor is sat very high on the transom in my opinion. The anti ventilation plate is a good 50-60mm obove the keel line (bottom of hull).

The previous owner says it worked well for him...

I am worried about loosing grip on the water with the prop (ventilating) (prop size 9.9 x13)

or even cooling water not getting in.
Should I be worried, or will it be OK. Should I lower motor by cutting transom or change motor for a longer reach ££££, which I am reluctant to do having just spent 1000'S on it, and its as new.

Why did ( or even did they??) a well know south coast boat company ( The wolf rock boat company........) supply and fit this outboard so high?? Was this a mistake or has the motor been changed? Paper work says this was the original motor..

I can cut the transom down, but this seems drastic to me on such a new nice rib... should I just try it?

Any input or opinions/suggestions will be welcome...

uncle al · 18 December 2012, 11:44

I am sorry there is no quick fix on setting an obm on any boat , it is all try and adjust, as for cutting the transom down that would have to be the very last chance, as a rule of thumb the cavitation plate should be level with the btm of the boat with a aluminium prop , but could be slightly up from the btm of the boat with a stainless steel prop, its all trial and error, good luck

PeterM · 18 December 2012, 11:47

Is there scope to move the motor down on its mounting bolts? I'd say try it out, see how it is then think about how it can be moved if needed without cutting or drilling anything?

Mextli · 18 December 2012, 11:49

I'd say... Try it! Get it on the water, have a go, and see if it works.

willk · 18 December 2012, 11:55

I'm curious as to why you are asking these (excellent) questions AFTER you purchased the RIB?

IIWY, I would phone Wolf Rock and (nicely) ask if they fitted the motor (good to know anyway) and if the height was determined by them or did the buyer spec or supply the motor fitted. You'd be AMAZED at how many people INSIST on fitting a wrong sized motor (HP or length) to a new RIB...

If the motor is confirmed as fit for purpose, then I'd test the RIB and watch the telltale during use. You'll need full trim down for turns, most likely. Why would you butcher a transom without testing it??

What IS the shaft length on the motor? S, L, XL?

thomas · 18 December 2012, 12:24

Take it out and see where the plate sits in the water when you're on the plane, I had to lift a motor a good few inches to get it working properly.

50mm doesn't seem that high to me, have a search on here, there's been quite a lot of discussion recently.

simsy · 18 December 2012, 12:35

Thanks guys!

I would not cut the transom with out testing and failing badly..
I bought the boat as it was a good price and as new. The subtle issues come out in the wash / in the eating of the pudding etc.
I could not of walked away from buying this boat, its mint.....

This is about tuning and performance/reliablity.... I do not regret buying it, and the gentleman that sold it says it runs well and I believe that is his opinion.

Maybe the boat was setup to run a stainless prop....... An aluminium one is fitted now.

No room to move the motor down on its bolts as in the lowest slots, and it is sitting on ther clamps also...

I will only cut the transom down as a last resort if the boat is poor on water etc.... and after much thought..

thanks again. any more ideas welcome, as I have months before the weather is good again....

I will check the motor length, but seemed to be around 18 inches (not a real size.) early days as I only spotted the issue last night after the guy buying my old engine (different boat) asked questions about the old boat transem height by text..

simsy · 18 December 2012, 12:48

IMG_1344_zps5b516773.jpg photo by simsy1962 | Photobucket

viking61 · 18 December 2012, 12:52

I wouldn't hesitate to call the guys at wolf rock , they were very helpful to me and did an excellent job on my ribtec refurb and motor install. IMO they really know what they are doing

willk · 18 December 2012, 12:54

That looks like a short shaft motor. The specs are here

There isn't much freeboard with that transom so fingers crossed she runs well as it is.

Johnscubanut · 18 December 2012, 12:57

Hmmmm, it does look very high on the transom. I always believed the cavitation plate should be roughly level with the bottom ot the keel?
Best to try out first tho & see if it ventilates?
If so, the engine may be a 'short-shaft' model. I believe you can get a kit to extend the length of the engine.
I wouldn't go cutting the transom down just yet!
Good luck!!

willk · 18 December 2012, 13:02

...and the specs for the 410 are here, it is designed for a long shaft motor. However, IIRC, Tohatsu shorts have a "tendency" to be a bit longer than some others. You may find that it works just fine. If not, I'd trade the motor before I'd touch that transom. You'll pay the price at sale time if you do...

simsy · 18 December 2012, 13:03

There are 3 more photos of boat in the bucket if you go right... above...

simsy · 18 December 2012, 13:13

I agree, cutting the boat up is a last resort. As I said, the last owner ran the boat and states it ran very well only 'cavitating' when on full power and a very hard turn.

Looking forward to using the boat, and hoping I get reasonable performance for a 30hp. Owner stated he saw 25 - 27 knots on the GPS. (low drag setup, lol....

two stroke mick · 18 December 2012, 13:34

I would be more concerned about how you are going to fit the tow bar to the green car given the location of the exhaust

Bet of luck with the new purchase

Locozodiac · 18 December 2012, 14:04

Definitely previous owner purchased a short shaft engine for a long shaft transom, had exactly the same issue as yours. In flat calm waters and near straight course no problems, excesive ventilation issues on choppy seas and close tight turns. In my particular case ended chopping transom down to match my Tohatsu to my 420 rib.

Chopping transom down would be the last resort for rib/engine to perform as expected, as probably impossible to change engine for a long shaft. The only small issue I find using a chopped down transom is slight water comming at transom area when reversing engine, a matter to reverse with less throttle. Other than that the combo flies with just a 18 horse. If needed can post pics of the modification.

Happy Boating

simsy · 18 December 2012, 14:49

''as probably impossible to change engine for a long shaft'''

what do you mean / why do you say this?

I would like to see your installation. Only 110 - 120kg base boat weight, so massive power not neccessary.....

sold the green car days after buying this boat.... never told new car owner is was a tow car...lol....

jyasaki · 18 December 2012, 16:25

Quote:

Originally Posted by Johnscubanut

Hmmmm, it does look very high on the transom. I always believed the cavitation plate should be roughly level with the bottom ot the keel?

I've always heard that's a starting point.

Once you get the motor mounted, it's trial and error tweaking stuff until it works for you. I've seen some boats run with the anti-ventilation plate way above the keel (and some that need to be a bit deeper.)

jky

thomas · 18 December 2012, 16:39

Here's an image of my old Valiant, I had the opposite problem, the engine was too low in the water and I was getting vertical fountains of water and pretty poor performance, every time I raised the engine things improved and then I ran out of holes, I ended up an inch higher that shown here.

As far as I'm aware the cavitation plate needs to sit level water line left by the back of the boat, too low and it will either cause drag or raise the back out of the water and make it less stable.

Your's doesn't look too bad to me, if it is wrong then buy a new motor before you get your chainsaw out, as soon as you start hacking it will be worthless. You can convert some motors between long and short shafts and it's not as expensive as you might think as long as the parts are available and you've got some basic common sense.

Locozodiac · 18 December 2012, 21:23

Quote:

Originally Posted by simsy

''as probably impossible to change engine for a long shaft''' what do you mean / why do you say this? I would like to see your installation. Only 110 - 120kg base boat weight, so massive power not neccessary.....

Was reffering that you have a short sgaft engine when needing a long shaft one, so probably changing, selling, buying a long shaft engine is not the way to go for you.

In my particular case my rib's keel to transom distance is 46 cm, this gave excellent speed in flat calm waters at straight courses, excesive ventilation at choppy seas and tight turns. Chopped transom dowm 5 cm to 41 cm and rearranged both engine plates to transom level, have reached the best transom height for best speed and inmaculate tight turns at wot. Engine is reving at 5600 (top is 5800) at 40 Km/h. My rib/engine combo weights 150 Kg.

Is not that Tohatsu has a larger lower leg, it's just it's tail design, a bit different that other brands lower legs. The distance stated on owners manual is just a refference from where to start, if you want ribbing perfection you need to fine tune engine height, most people just sits engine matching same size leg to same size transom and that's it, but are losing the best engine performance that can be taken out from any engine.

Trimming engine all the way down is no the way to go, rib will tend to bow excesively down. With engines that dosen't have electric trims you just need to have engine sitting perpendicular with a well ballanced boat. No need to be constantly playing with trim. This is the perfect height for your engine, check video.

Tohatsu 20hp w/ 3/4" shim and proper trim - YouTube

Happy Boating