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Old 27 May 2018, 09:56   #1
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RIB trim bow high?

Hi all, I was out on my RIB with an experienced mate and he was of the opinion that she rides high at the bow (max weight engine on the transom and slightly aft of midships helm position) and suggested I have the outboard trimmed fully in all the time to compensate. I'm fairly new to RIB's so I don't know too much about what the attitude should be but am not completely happy about having the leg trimmed fully in all the time as it leaves me nowhere to go. I am starting to think trim tabs might be the answer, what do you think, is she bow high? I have attached a short video of her planing at about 20 knots.
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Old 27 May 2018, 10:28   #2
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Cant see your video but if your sat at 20kts with the bow high maybe you need to cruise faster? My hard boat doesnt like much less than 25 kts or the arse sits in the water get over 25kts and its fine
Presumably if your on max weight your also on max hp? Does that allow you to travel faster if you want to?
Have you tried running faster to see if the attitude improves?
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Old 27 May 2018, 10:58   #3
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Riding bow high can be due to many things, hull design, weight distribution, having the engine set too low on the transom. Etc.
There are as many remedies, it might be supposed to run like that, boats with a high sheer bow tend to look arse heavy, Deltas & Ribcrafts spring to mind. The "flatter" hulls tend to look lower on the bow, Avons & some Humbers e.g.
Without knowing what you have it's difficult to make a judgement, your mate might not be familiar with the ride characteristics of your hull.
If it is riding high, you could try the good old 25kg bag of sand in the bow locker, lifting the engine, different props (some are "bow lifting" others are "Stern lifting")
Trim tabs will solve the problem, if there is one, but are a significant cost.
Also in my experience, shorter hulls are more susceptible to riding high due to weight distribution, you have less scope to shift weight around in a smaller boat & due to the mechanical moment a small shift in weight makes a big difference to the balance.
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Old 27 May 2018, 11:09   #4
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Hi beamishken, yes the outboard is max hp (115) and she has max speed of 40 knots, I've taken her to just over 30 since I've had her and the attitude seems to stay the same, but of course if I trim in and open her up then the extra thrust will push the stern up/bow down. I'll try and post the video again.
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Old 27 May 2018, 11:34   #5
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Thanks for the reply Pikey Dave, you make some good points there (as usual). Stuff to think about.
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Old 27 May 2018, 11:39   #6
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As Dave says many variables id start with the easy stuff like moving gear about and see if it helps.
Trim tabs will help lift the stern but i only use them to get on the plane then fully retract once on top otherwise its a bit like running with the handbrake on.
Is the trim limit pin in the last hole or is the transom particularly straight? Maybe a picture of the boat out of the water with the engine trimmed down might help
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Old 27 May 2018, 14:38   #7
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Thanks Ken, I keep the boat in Portugal where we winter so won't be back with the boat till September when I can check out your suggestions re trim pin etc.
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Old 27 May 2018, 15:40   #8
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G.G. I looked at your video and IMO you should have the bow somewhat higher underway. I suspect that your friend is a yachtie?

BTW, you should open your throttle up and explore the various trim possibilities your boat has to offer - maybe bring an experienced powerboater along for a look-see.
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Old 27 May 2018, 16:15   #9
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Thanks for the reply willk, you are spot on, my friend lives, and is an RYA instructor in Portugal on the Algarve. His first love is sailing I'm sure, but he instructs on various RYA courses including Powerboat level 2. Out of interest what led you to the assumption he was a yachtie?

I take your point about trying different speeds/trims which I fully agree with, can't beat suck it and see. Only managed to get about 20 hours this year but when we go back in September I intend to spend a lot more time boating/getting to know my RIB.

BTW I assume you managed to view the video cos you are Admin, any idea why we can't view it on the forum?
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Old 27 May 2018, 16:23   #10
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Originally Posted by Grant Garwood View Post

any idea why we can't view it on the forum?
It's because the forum video option is gubbins, best using youtube.
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