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Old 27 August 2019, 04:18   #1
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Rib Nose up???

Can anyone help. I have a 4.2m rib with a mercury 60 four stroke. When in harbour at 6knts it sits nice and flat. Above this the nose sticks up ridiculously Like itís trying to push under itself until it planes. Can anyone offer advice regarding engine position/trim/anything to improve this. If I try to pull a skier out the whole (heavy 95kg sods like me) the boat pitches nose up and struggles to get on the plane and acts more like a damn!

Engine height? Up or down? Would this help? All technical/practical advice appreciated.
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Old 27 August 2019, 04:26   #2
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Hydraulic or fixed trim?
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Old 27 August 2019, 04:37   #3
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Quote:
Originally Posted by cheeseboat View Post
Can anyone help. I have a 4.2m rib with a mercury 60 four stroke. When in harbour at 6knts it sits nice and flat. Above this the nose sticks up ridiculously Like itís trying to push under itself until it planes. Can anyone offer advice regarding engine position/trim/anything to improve this. If I try to pull a skier out the whole (heavy 95kg sods like me) the boat pitches nose up and struggles to get on the plane and acts more like a damn!

Engine height? Up or down? Would this help? All technical/practical advice appreciated.
I assume the engine isnít too heavy......and the weight on the boat is at least central or preferably forward.....and the motor is trimmed in....if those basics are ok you may need to look at fitting some wedges for the engine mounts.... itís also asking a lot for a 4.2 m boat to be comfortable in pulling out a95 kg skier..
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Old 27 August 2019, 04:45   #4
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Right leg length.....L, XL..? Prop set too deep ?.
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Old 27 August 2019, 05:02   #5
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Hydraulic or fixed trim?


Thanks for responding

Itís hydraulically trimmed. Trimmed full down.
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Old 27 August 2019, 05:04   #6
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I assume the engine isnít too heavy......and the weight on the boat is at least central or preferably forward.....and the motor is trimmed in....if those basics are ok you may need to look at fitting some wedges for the engine mounts.... itís also asking a lot for a 4.2 m boat to be comfortable in pulling out a95 kg skier..


I think yes to those basics but need to check properly.

So would wedges to push the top of the engine back be worth a try?
I never need to trim up when planing.
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Old 27 August 2019, 05:05   #7
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I think yes to those basics but need to check properly.

So would wedges to push the top of the engine back be worth a try?
I never need to trim up when planing.


And yes, I appreciate itís asking a lot! I would loose weight but drinking and eating too much is for more inviting 🤣🤣🤣
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Old 27 August 2019, 05:07   #8
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Originally Posted by Last Tango View Post
Right leg length.....L, XL..? Prop set too deep ?.


The ďventilationĒ (I thinks thatís what itís called) plate (the bottom flat fin) is roughly level wth the bottom of the transom.
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Old 27 August 2019, 05:36   #9
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The centre of gravity may be too far back I had same problem with my 4m Avon.with a 4stroke 40HP
On plane engine should be trimmed up c.halfway

I'd move what weight I can -batttery, fuel, etc. forward & see what effect that has.

Have you considered fitting Doelfins? - I found they made a huge difference.

Think about some ballast in bow as a further option

LT
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Old 27 August 2019, 05:59   #10
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RIBase
very low powered engine to pull a 95Kg skier but it sounds like you have other issues at play to sort out first.
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Old 27 August 2019, 06:49   #11
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Originally Posted by lakelandterrier View Post
The centre of gravity may be too far back I had same problem with my 4m Avon.with a 4stroke 40HP
On plane engine should be trimmed up c.halfway

I'd move what weight I can -batttery, fuel, etc. forward & see what effect that has.

Have you considered fitting Doelfins? - I found they made a huge difference.

Think about some ballast in bow as a further option

LT


Thanks LT, really helpful. Iíll try all these tips.
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Old 28 August 2019, 04:14   #12
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I have the same problem with my little 330 rib, 15 hp. All I have to do is send the passenger forward and away it goes
So it's probably a weight problem.
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Old 28 August 2019, 04:28   #13
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not got water in the hull if thats the type of design, it should have a drain plug at the stern
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Old 28 August 2019, 09:16   #14
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I would recommend "automatic" trim tabs, whatever brand you prefer. I have nauticus smarttabs on my rib and without them I can't get on plane with only me. It's too stern heavy.
They are spring loaded so they self retract when you get on plane. They have a chart on their website to fit the right spring strength.
You can also get a kit to manually retract them so they are not in the way for trailering. Sometimes I forget to put them down coming off the trailer and I instantly know whats wrong.
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Old 28 August 2019, 14:37   #15
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I have a 4.2m zodiac pro with Yamaha 40hp 2 stroke. I weigh 85.3kg and the rib pulls me out with ease and that includes 3 adults on board. So not convinced there is a power issue. Like your rib when in harbour it rides very nose high and nose high before going on plane. In my case it’s definitely a weight distribution problem. Mine is back heavy and I bet yours with a 60hp 4 stroke will be too. Move bodies (weight) up front and this significantly reduces the nose up for me. Mine is a jockey seat with anchor spare fuel all up front. 40litres fuel and battery under seat. Still rear Heavy. Apart from adding permanent weight up front (or making people go up front (if they are on boar) until on the plane) the only other solutions/improvements I can see might be the use of the dolphin fins or the auto trim tabs mentioned by others and I haven’t tried either. I’m tempted tho. But your not alone. Good luck.
Bremar
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Old 28 August 2019, 18:09   #16
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not got water in the hull if thats the type of design, it should have a drain plug at the stern
Definitely worth checking
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Old 29 August 2019, 02:08   #17
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Originally Posted by Bremar View Post
I have a 4.2m zodiac pro with Yamaha 40hp 2 stroke. I weigh 85.3kg and the rib pulls me out with ease and that includes 3 adults on board. So not convinced there is a power issue. Like your rib when in harbour it rides very nose high and nose high before going on plane. In my case itís definitely a weight distribution problem. Mine is back heavy and I bet yours with a 60hp 4 stroke will be too. Move bodies (weight) up front and this significantly reduces the nose up for me. Mine is a jockey seat with anchor spare fuel all up front. 40litres fuel and battery under seat. Still rear Heavy. Apart from adding permanent weight up front (or making people go up front (if they are on boar) until on the plane) the only other solutions/improvements I can see might be the use of the dolphin fins or the auto trim tabs mentioned by others and I havenít tried either. Iím tempted tho. But your not alone. Good luck.
Bremar


Thanks for replying. I understand and agree. The only thing on your side is the instant power of the 2 stroke. Iím going to try some weight shifting and also the wedges to see if I can use the engine to improve the stern lift. This should also give me some trim when Iím planing as I currently donít have any need to. If that doesnít work Iíll try the fins or tabs. Iíll report back so all who have offered help can read the results if your interested.
Thanks again
Cheeseboat.
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Old 29 August 2019, 02:09   #18
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Originally Posted by babbot1 View Post
I would recommend "automatic" trim tabs, whatever brand you prefer. I have nauticus smarttabs on my rib and without them I can't get on plane with only me. It's too stern heavy.
They are spring loaded so they self retract when you get on plane. They have a chart on their website to fit the right spring strength.
You can also get a kit to manually retract them so they are not in the way for trailering. Sometimes I forget to put them down coming off the trailer and I instantly know whats wrong.


Thanks. Iíll try these if the wedges donít do it.
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Old 30 August 2019, 03:46   #19
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Try a 4 blade prop thatís helped me. Now it just hops up onto the plane
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Old 31 August 2019, 02:49   #20
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Try a 4 blade prop thatís helped me. Now it just hops up onto the plane
Same pitch?
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