RIB trim bow high?

[Grant Garwood]

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.

[beamishken]

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?

[Pikey Dave]

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.

[Grant Garwood]

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.

[Grant Garwood]

Thanks for the reply Pikey Dave, you make some good points there (as usual). Stuff to think about.

[beamishken]

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

[Grant Garwood]

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.

[willk]

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.

[Grant Garwood]

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?

[Xk59D]

Originally Posted by Grant Garwood

any idea why we can't view it on the forum?

It's because the forum video option is gubbins, best using youtube.

[Last Tango]

Originally Posted by Xk59D

It's because the forum video option is gubbins, best using youtube.

Yep.

Can't even get it to run with VLC

However, looking at the "still frame" the trim looks pretty much bang on

[Pikey Dave]

It did play briefly for me earlier & it looks like a high bow hull, there’s a definite “crank” in the tube line from midships to the bow. It looked reasonable to me, nothing that a bit of tweaking shouldn’t sort out. I’m guessing that its a pretty shallow hull that won’t have much in the water to start with.

[jwalker]

For a smooth water run, I'd say your hull looks pretty well spot on. Your pal is a numpty.

If it gets rough, you may need to trim in a little to hold the bow down but that is normal.

[Searider]

Originally Posted by Grant Garwood

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.

Looks OK to me.
I think your friend may not have noticed how much of a sheer your tubes have. From inside the boat it will look like you're running bow high.
I have this with my Scorpion. I find it very disconcerting if I drive a boat with "straight" tubes - it feels like i'm about to trip over!

[Grant Garwood]

Thanks for all the replies guys, I feel much more comfortable with my "high bow" now. Still might get some trim tabs though, can only improve things surely

[Last Tango]

Originally Posted by Grant Garwood

Still might get some trim tabs though, can only improve things surely

Just bring a whole new set of problems....If it ain't broke, don't fix it.