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Old 24 April 2011, 16:16   #1
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Newbie needs advice - Valiant PT520

Hi all
I'm new to Ribs and have just bought a Valiant PT520 with a 2 stroke 90hp Saltwater Mercury. It has a "Vortex Miwheel 13 x 19" prop on it and with 2 adults on board only does 28 knots, 33mph according to the gps, is this about right guys, I thought it would go faster? the engine runs fine. I've read some of the other posts on speed and it does seem slow for this size/power rib. Also when I tilt the engine it can be tilted so far as to push into the back of the boat, it there a way to limit the amount of tilt? One last question, if you let go of the helm whilst planning it pulls hard to starboard, you have to almost fight with the wheel to keep it straight, its quite dangerous and could throw someone out if caught out. Any sugestions on how to cure this? I'm the 2nd owner, it was bought new from a boat show and towed away from the show, I suspect it has never been set up right, I've had to realign it on it's trailer as it was not sitting anywhere near correctly. I want to get familiar with the Rib and be able to maintain it myself. Like I say I'm new to Ribs and any advice would be much appreciated.
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Old 24 April 2011, 17:00   #2
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I'd suggest an RYA level 2 course where you will learn about trimming the engine for best speed and control for cornering (without fighting the helm).

As for speed it does sound a bit low, which could be a number of things - wrong trim, wrong prop, water in the hull void, engine not getting to max rpm etc. What revs are you getting?
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Old 24 April 2011, 17:13   #3
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Changing the propeller size pitch can help. However you need to know the rev range of your engine. If it's short of its maximum operating range, then you have some options. As a general rule of thumb, dropping the pitch size by an inch will increase revs by 200rpm. If you can borrow a suitable propeller (17" then that might by the way to go). In addition, the height of the engine can be increased marginally (so the anti-cavitation plate is raised slightly above the hull of the boat.)

Regards the trim/tilt. On some engines (Tohatsu for example), there's a stainless steel strainer wire that limits the tilt. Could be something that could be adapted on your Mercury?

Lastly, pulling to starboard. Is the engine offset? Normally only an issue on larger engine outboards. Did a bit of digging and found this old post from 2004. Similar boat and engine size, and they offset it 2 inches to get it to steer straight. http://rib.net/forum/archive/index.php/t-7935.html

Before drilling new holes, I'd check if it has been offset already and get a little more feedback from members with a similar setup. Check the trim-tab too. Sometimes a little adjustment works.
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Old 25 April 2011, 04:43   #4
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Lastly, pulling to starboard. Is the engine offset? Normally only an issue on larger engine outboards. Did a bit of digging and found this old post from 2004. Similar boat and engine size, and they offset it 2 inches to get it to steer straight.
I'd think this is more likely related to incorrect trim, see ChrisHowden's post of a few weeks ago (and other people have had similar issues).
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Old 25 April 2011, 11:08   #5
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It sounds as though you don't have NFB (no feedback steering) fitted, NFB eliminates the torque steer you feel pulling the wheel.
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Old 25 April 2011, 12:26   #6
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Thanks for all the advice guys. I'm looking into some RYA training and have had some good tips, i'm hoping my steering issue is incorrect trim, I've had some good pointers on how to cure it. Much appreciated all.
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Old 26 April 2011, 08:05   #7
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Originally Posted by Sea Ray View Post
Also when I tilt the engine it can be tilted so far as to push into the back of the boat, it there a way to limit the amount of tilt?
Is there not a big pin goes through two of a set of holes in the bottom of the clamp brackets? If so, you can move it out to limit the downward travel. If not, you probably need to go and buy a replacement pin!

Item 4 on the diagram here, move it up the curved row of 6 holes on the bottom of the bracket. http://www.boats.net/parts/search/Me...KET/parts.html (doesn't matter if this isn't your engine, they all have a variation on that theme......)



For what it's worth I can't think of any boat I've ever used that had the pin on the "full down" position.
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Old 26 April 2011, 14:58   #8
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Apologies I did not make myself clear on the tilt issue. It's when I tilt the engine up to bring it out of the water, the engine can be tilted so high that the front of the engine hood can hit the top of the boat, the area in front of the engine, usualy a bit of a water trap where the various hoses and cables gather. I'm not the only one to use the rib and if the engine is tilted fully without taking care it can (as it has already done) score the engine hood and the boat. I'm looking for a way to restrict its upward tilt. I did check for a pin to limit it's downward travel and there is not one. I'm guessing this is because the hydralic trim has a trim indicator at the helm so you know where it is.
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Old 27 April 2011, 04:23   #9
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No worries, We all know what we are writing about!

Tilt up stops usually are down to the ram running out of travel. I think some really old systems (the 1960/70's Outside ram type) used an upper stop switch, but usually it;s just the ram that canlt physically go any further.

Two options are an electric switch that will open & cut power to the pump or as you said, a wire to the leg. The switch would likely be neater, but at the same time introduce another electrical failure possibility. I guess you could rig a wire hawser to pysically stop it, then the pressure relief valve i nthe unit should open.

I'd try & replace that down stop pin, as it does give the leg something to brace against shoud the PT fail.
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