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Old 25 May 2004, 20:40   #1
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Country: Norway
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Engine: Inboard Volvo Penta D3-160
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Cavitate problems: Humber 8m w/Volvo D3-160

Hi.
Just received my brand new Humber Ocean Pro 8,0 meter a week ago. I have been installing the new Volvo D3-160 engine in the weekend and done some testdrives. The boat feels very stable and it performs very well especially in rough seas. It actually eats the waves and it makes it a very pleasant ride.


CAVITATION PROBLEM:
The drive has to be in the maximum "down" possition to be usefull. If I use the trim for 3 degress up or more it starts to cavitate and it looses grip of the water. The same happens when doing very sharp turns.
Since this setup never has been delivered from Humber and I am living in Norway they are not able to testdrive it and come up with a solution.

The cavitation plate are some few centimeters above the keel and I do have som few theories. Maybe some of you guys out there have experiences or other ideeas about how solving my problem.


TESTS:
- LOAD ON SEATING: 2 passengers in jockey and 1 on the engines housing. This solution gives us some very few steps up to play with on the trim before it loose grip of water. (working area from -9 to – 6 degrees on drive). It feels like we have lots of power and it is easy to enter max rev at 4000rpm

- LOAD IN FRONT: 2 passengers in the bow and driver seated in jockey. This gave us nothing extra and it felt even worse than when everybody was seated in jockey and on engine housing. There was problems with using the trim in other positions than the max down/in position.. (working area from -9 to – 8 degrees on drive) It feels like enough power and reach 4000 easily.

- LOAD REAR: We moved the 2 passengers back to the transom and it gave us extra trim possibillities and it felt like more speed.
(working area from -9 to – 1 degrees on drive). It feels like enough power and reach 4000 easily.

- MORE LOAD: We was trying with 5 persons aboard and it felt like we were more heavy loaded. The RPM stopped at around 3800-3900 RPM with this load. It was getting late and we were not able to do more tests with 5 persons. Hopefully more testing tomorrow. It feels like it was a bit more heavy and we was not able to get 4000rpms.


SOLUTIONS ???:
We do understand that there can be several reasons for these problems and we have listet some of our teories here:



o Problem: The Sterndrive is installed to high.
Solution: Buy a “add-on ” kit that makes the drive go 2-4 cm deeper in the water. This is some kind of spacer to put on.



o Problem: Wrong propeller
Solution: Find a propeller that fits the setup better. Do you have any experiences about a bigger or smaller propeller will give less “spinning” (loose grip) in the water???? A thought might be that a propeller wit smaller diameter will stay further down into the water. On the other side will a bigger propeller have more grip in the part staying under water. I suppose that there are some propeller experts out there.



o Problem: Something disturbs the waterstream
Solution: Move the item that makes problems. The Water inlet are installed as Volvo described it. Aprox 70cm from transom and around 27 from the keel on the right (starboard) side (Volvo recommended min 60cm and min 20cm)



o Problem: Hull disturbs the waterstream (Not 100% straigth keel):
Solution: When we saw the boat on land we noticed that the keel was not 100% straight in the first meter from transom and forward. From the keel as the lowest point it bent a bit (some few mm) upwards further forward. This might make a stream pushing the water down under transom and resulting in the prop loosing grip of the water. We did not measure this, but just did a visual estimate.


We are willing to buy more than one propeller to fit our needs:
Prop A) Heavy load: totals 2550 kg (1000+200+15x75)
Prop B) Light Load: totals 1500 kg (1000+200+4x75)
Prop C) All round: Optimal and good between 1700-1900kg (1000+200+8x75)


Any advice and suggestion will be very apreciated.....

Regards Steve Michael, Norway
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Old 26 May 2004, 02:38   #2
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Country: UK
Boat name: Seascaper
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Hi Michaels,

Sounds like you have a problem. I had a boat built a couple of years ago by a company who had had no experience of fitting twin outboards and it was a complete disaster and I could not accept it. The engines were fitted too high and had similar problems to the ones you have. Changing the props did not help the boat was dismantled and taken apart.

I am out here in Norway at the moment -Arundal where I test drove the prototype Goldfish 25 at 65 knots. Great boat.

Lester
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Old 26 May 2004, 03:14   #3
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Quote:
Originally Posted by Michaels
The cavitation plate are some few centimeters above the keel and I do have som few theories. Maybe some of you guys out there have experiences or other ideeas about how solving my problem.
The cavitation plate (technically the ventilation plate) should be below the keel not above it; otherwise when going fast it will be out the water and hence not doing much.
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Old 26 May 2004, 04:20   #4
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Steve

From what you have said I would guess that the sterndrive is too high. The improvement by loading the stern of the boat supports this theory.

If it was something disturbing the waterstream then I would expect it to happen whatever the trim. It is unlikely that changing the prop will help.

In high speed outboard applications it is not uncommon to have the ventilation plate a couple of centimetres above the keel, but in your case I would certainly not expect to see this.

Humber have installed D3s before, so I would have expected them to be able to advise.

At least there is a kit that may easily solve the problem though. I had an outboard powered RIB with similar symptoms and the only solution was to cut about 50mm off the top of the transom!

Let us know how you get on. I would be very interested to know what sort of speeds you are getting with this boat/engine combination.

John
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Old 26 May 2004, 07:50   #5
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Quote:
Originally Posted by Michaels
Hi.
o Problem: Hull disturbs the waterstream (Not 100% straigth keel):
Solution: When we saw the boat on land we noticed that the keel was not 100% straight in the first meter from transom and forward. From the keel as the lowest point it bent a bit (some few mm) upwards further forward.
This is normal for the boat.

I agree, you probably need to fit the spacer kit.

---------------------------------

Quote:
The cavitation plate (technically the ventilation plate)
Technically, the anti-ventilation plate.
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Old 26 May 2004, 08:34   #6
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When we saw the boat on land we noticed that the keel was not 100% straight in the first meter from transom and forward. From the keel as the lowest point it bent a bit (some few mm) upwards further forward.

Quote:
Originally Posted by jwalker
This is normal for the boat.

I agree, you probably need to fit the spacer kit.

---------------------------------



Technically, the anti-ventilation plate.
Hi there!
Quick question re the keel not being straight. I read in one of the threads previously about a problem developing when the hull extended too far over the end of the trailer and resulted in a concave shape forming. How is this different to the characteristics of the keel above? I'm probably confusing myself, but hopefully an explanation will put me right.
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Old 26 May 2004, 14:39   #7
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I don't know why Humber have chosen to do it, but they do. It simply creates a bit of stern lift. They had a bit of criticism of the early boats travelling bow high. My guesses are; 1) the very high bow needed a bit of control or, 2) they bu**ered up the mould.

It is slightly different to the sagging caused by bending on a trailer because that makes the flats of the hull hollow.
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Old 26 May 2004, 17:34   #8
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Hei! Jeg har en 8.75m rib med 2 x250hk og har kavitert masse. Jeg har løftet og senket motorne og prøvd store og små propeller.
Det er ikke størrelsen på propellene som avgjør om de kaviterer, men formen. I tillegg er jo noen propeller laget som overfflatepropeller. Ta kontakt med noen som er dyktige på propeller. En mindre propell med flere blader, gjerne 4 kan være en løsning. Ta kontakt med Matt på Throttle-up.com. Han sitter i USA, og svært dyktig. Han trenger alle opplysninger du kan komme på.
Har du hjemmeside med bilde av båten?
Ha en fortsatt fin dag! (ps. hvis du skriver .no bak mit alias, så kommer du på hjemmesiden min.)
Martin
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Old 26 May 2004, 17:47   #9
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Quote:
Originally Posted by Fjordrafting
Hei! Jeg har en 8.75m rib med 2 x250hk og har kavitert masse. Jeg har løftet og senket motorne og prøvd store og små propeller.
Det er ikke størrelsen på propellene som avgjør om de kaviterer, men formen. I tillegg er jo noen propeller laget som overfflatepropeller. Ta kontakt med noen som er dyktige på propeller. En mindre propell med flere blader, gjerne 4 kan være en løsning. Ta kontakt med Matt på Throttle-up.com. Han sitter i USA, og svært dyktig. Han trenger alle opplysninger du kan komme på.
Har du hjemmeside med bilde av båten?
Ha en fortsatt fin dag! (ps. hvis du skriver .no bak mit alias, så kommer du på hjemmesiden min.)
Martin
Translation: (Not sure its that much clearer!)

hello I've a rib along with 2 x250hk and has kavitert a lot of. I've lifted and was lowering motorne and attempted big and a little propeller. That is not bulge at propellene as decides about they kaviterer , but fitness. Additional am certainly a few propeller layer as overfflatepropeller. Get contact along with a few as am capable at propeller. A less propell along with more leaves , certainly 4 can be a answer. Get contact along with Matt at Throttle -up.com. He sit in USA , and mighty able. He need full particulars you come about. Have you hjemmeside along with picture at the boat? Have a continued fine day! (ps. of which you draw up.no at the back mit alias , saw comes you at hjemmesiden min. ) Martin
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Old 26 May 2004, 17:52   #10
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So basically he's saying a prop change should be able to sort it and to
speak to matt at http://www.throttle-up.com?
I've spoken to julie (matt's wife) before and she was very friendly and helpful. They are sponsors of offshoreonly.com.

I think basically Mr K is right, for the prop you're running it's not deep enough. What prop is currently fitted?
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