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Old 17 June 2018, 01:45   #1
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Country: USA
Town: Anchorage
Boat name: Poor Pecos
Make: Inmar
Length: 4m +
Engine: Suzuki 25 hp
Join Date: Aug 2017
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First outing....I have questions

OK. Thanks Gents for all the info I have enjoyed and benefited from all Winter. Now I have my boat, a 14ft SIB (Inmar) - that is 4M I believe, and with a 25 hp Suzuki. Will be in Prince William Sound in July for a Small 8 mile trip up Passage Canal. Have been learning a ton in local lakes to prepare. Here is where I am stumped.

1. When I get to speed (just me and my two teen daughters, little gear) on a plane WOT I have had the experience of feeling like we have run over something. A big bump, throws us up it feels. First time I really thought I had gone over a log or something, but no. Girls thought I hit an animal, thatís the feel. Not hitting anything. Quite frightening actually. Floorboards kinda rumble and the bow kicks up violent like, but all is structurally sound. Stringers holding joints, floor not buckling. What the heck is going on? Has happened several times. Flat calm, maybe a ripple on the lake. Doesnít happen every time, but enough to make me not run at speed often.

2. My engine is throwing water in the boat at WOT. Normal? The kick back from the propeller is somehow throwing in the boat. While I sit on the tube to throttle Iíd just get soaked from the kickback. Have tried various tilt action on motor, all does the same.

3. One more please. I try to tilt up a bit to play with trim, but when I get to speed the tilt is lost. I can see the engine gradually dig back in, losing my tilt, even though I have locked in place. What gives.

First boat. Having a blast. Be gentle, but shoot me some information please. What am I not getting on these ones?
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Old 17 June 2018, 02:51   #2
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1 & 3.....

Don't confuse trim & tilt.

Only the bottom part of the movement on most engines is actually "trim".
Beyond that is "tilt". Could it be you're trimming way out into the "tilt" part of the movement and the "thump" you feel is the engine dropping back to the "trim" part when you throttle up.

I'm not familiar with your engine but most larger engines will drop back to their maximum "trim" position if you push them beyond a hard idle if their tilted too far out. This is both for safety and to protect the engine from damage.
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Old 17 June 2018, 03:38   #3
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1/ Sounds like the boat isn't up to pressure and you're displacing water rather than planing. Not familiar with Inmar inflatables, but you mentioned stringers, so assume build is similar to Zodiac. The inflatable keel on Zodiacs MKII (4 meters) is 220 millibars and the sponsons were 220-240 millibars. There's no way the floorboards should 'rumble'. Double check with a pressure gauge, especially in the water as ambient temperature and the water temperature all play a part.

2/ With the boat out of the water, check the anti-cavitation plate is horizontal in line with the keel.

3/ I used to run a Zodiac MKCII (13'6") with a Yamaha 25hp. The engine was 2-stroke and manual start and tilt. In all the years I was running it I rarely tried to move the adjustment on it. It was set on the second hole away from the transom. With 3 people on board I doubt you have the horses to see any benefit from adjusting trim.

Anyway, see how you get on.
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Old 17 June 2018, 05:55   #4
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Hello and welcome to the forum.

It would help to know which Inmar model you have... the leisure or pro type? Does it have a sectional wood or alloy floor?

Re the outboard do you know if yours is the correct shaft length for the transom? Is it a new type Suzuki 25hp 4-stroke?
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Old 17 June 2018, 07:17   #5
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That's a moderately large SIB with what sounds like a light crew. One possibility is that air is getting under the bow and lifting the boat, then then it is slamming back down. My gut feeling from your description is that your engine is tilted too far out, which will tend to squat the stern and raise the bow and make make handling a bit squirrely.

The other thing to consider is that in any given set of conditions (sea state and direction, wind force and direction, weight of crew and equipment, weight and power of engine) there is an optimal maximum speed. Flat out is not always the best. Just because you've got a few revs left in the throttle, doesn't mean it's always the best idea to use them. Back off a bit and the boat may settle.

But first, look at how far out/down the engine is.
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Old 17 June 2018, 12:22   #6
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Country: USA
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Thanks so much:

Fenlander - It is a 430 Mil Inmar. Aluminimum floorboards 5 of them plus the bow. It is a short shaft 4 stroke, yes the boat requires short shaft.

Last Tango - Right. I see I need a vocab lesson. I thought tilt refers to how down or up I raise the prop in the water. I thought trim refers to how low or high the bow is riding. I’ll study up on the forum a bit more.

Spartacus- What is VAT? Good point on the pressure. I will check. It has over inflation relief valves and my guy said I don’t really need a pressure gauge. Just bring them up to tight with foot pumps to 3.5 psi. But the foot pump gauge seems silly. Can’t really tell what I’m at. I’ll get a decent gauge. And I haven’t messed with anything on the motor. Don’t know what an anti-cavitation plate is. I see I am using the word tilt wrong and throwing in some confusion. I was just referring to raising the prop or lowering the prop up and down. I still get water thrown in the boat no matter how I angle it. And - the motor won’t stay angled where I put it.

Mikefule- Thanks for that. Yes , ease up on the throttle may be the best idea. My 16 year old is having a blast and always wants faster - but I want safety and answers.

Thanks again guys. Incredibly responsive and helpful.
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Old 17 June 2018, 13:16   #7
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Quote:
Originally Posted by Snowmastiff View Post
...... - the motor won’t stay angled where I put it.......
How exactly are you adjusting this.....

Does it have power trim and the hydraulics are dropping or are you relocating the bracket pin of a manual trim system. If you have power trim the engine will only stay out to the maximum limit of the trim. Lifting it higher than that takes it into the "tilt" range and is only for lifting the prop out or nearly out of the water for mooring/trailering or for manoeuvring at very low speed in shallows.

If you're moving the pin of a manual tilt engine, the engine can't drop back down because it is limited by that pin. When the manual system is fully tilted there will be a latch of some kind on the bracket to hold it there but the engine can't be run in this position.

Maybe some photos of the engine tilted up would help.
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Old 17 June 2018, 13:29   #8
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Quote:
Originally Posted by Snowmastiff View Post
Spartacus - What is VAT? Good point on the pressure. I will check. Donít know what an anti-cavitation plate is.
It's just my signature - ignore it. In the UK we're paying 20% tax on purchased goods straight to HM Treasury so they can squander it!

Good news about getting a gauge. A foot pump doesn't really give you a proper reading.

The anti-cavitation plate or correct term is anti ventilation plate is on the outboard and stops air being drawn down down to the propeller. This diagram illustrates. You want the keel and anti ventilation plate to line up, give or take 25mm.
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Old 17 June 2018, 14:22   #9
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I had the issue with water splash back at WOT and it turned out the engine was too low on the transom.
There was no adjustment so l put a 1/2Ē thick block of wood on the engine mount to raise it and that stopped the splash back completely.

Zodiac 2.85s with Tohatsu 9.8
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Old 17 June 2018, 14:36   #10
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Re. point 1... I suspect the tubes and keel were not up to pressure. Was the water cold and did you top up the pressure when the boat was in the water? I have experienced similar issues with a 4.2m Zodiac late in the evening when the air temp. dropped and the water was rough, the pressure had dropped enough to allow the boat to flex and lose some rigidity.
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