First time with a 25hp o/board

kevinsc · 03 June 2017, 21:16

Hi all
I bought myself a 25hp suzuki df25 vtwin for my hydro force aluminium sib, I was at loch lomond using the o/b for the first time. At the start of trip went fine but halfway in the trip the sib felt like the back quarter felt like it was going down and sinking and the floor made a creaking noise like it was trying to bend it and then it felt fine, it did this a few times during the trip, it felt like the back of the boat wanted to go forward and the front didnt want to and had the brakes on. I check the air pressures and they were fine the weight in the sib evan, the only thing there was is about litre on water in the boat, the rubber valve looked like it was working. Is this normal or is there a problem l have to a dress.
Cheers kevin

jeffstevens763@g · 03 June 2017, 21:55

Kevin it's hard to understand your problem as you are finding I might be wrong but is your bow digging in if so where is your trim pin in the first hole? I assume you have the correct prop & engine length
The keel is solid
Tubes up to pressure etc.
You have a little water no problem that could be the the mushroom valve leaking a little in your drain valve
Weight distribution is equal.

kevinsc · 03 June 2017, 22:21

Hi jeff
Yes thats sounds like what its doing, the o/b is a short shaft and is straight, think the trim pin is in the first hole but to make sure where about is it.
Thanks for the help
Cheers kevin

Mikefule · 03 June 2017, 23:23

Are your tubes hard enough? Are all your floor panels in correctly? On one of my earlier SIBs, I once had a situation in which I was going fast and a floor panel slipped out of place causing the boat to go out of shape. If you are used to a smaller engine, it could be something like that: a poorly set up hull folding a bit under the pressure of more power.

However, most likely is that your engine is tilted in such a way that it is lifting the stern and causing the bow to dig in a bit.

It sounds unlikely to be weight distribution as I guess that your new engine is heavier than your old one, and that everything else is the same as before. If so, that would tend to make the bow rise higher rather than the symptoms you have described.

kevinsc · 04 June 2017, 10:12

Hi mike
I had a 5hp o/b before and no problems and I think with having more power means that I have to set it up better, the tube were at the correct pressure and floor panels correct I think the bow digging in a bit but not sure how to adjust the trim.
Cheers kevin

Mikefule · 04 June 2017, 15:05

If the bow's digging in it means that the outboard is lifting the stern.

If the outboard is lifting the stern, it means that the outboard is pitched wrongly.

The easiest way to think about this is that the outboard always tends to move in the direction of the tiller - to if the outboard is lifting the stern, the tiller is pointing too high.

If you tilt the engine then lower it again, you should be able to identify what it rests against. There is usually some sort of pin/bar which can be positioned in one of several holes. Move it to the next hole to adjust the trim.

kevinsc · 04 June 2017, 15:11

Hi mike
That makes sense I did wonder what that bar did, going to adjust the outboard and give it a try.
Thanks for the help will let you know how I get on.
Cheers kevin

jeffstevens763@g · 04 June 2017, 17:16

Quote:

Originally Posted by kevinsc

Hi jeff
Yes thats sounds like what its doing, the o/b is a short shaft and is straight, think the trim pin is in the first hole but to make sure where about is it.
Thanks for the help
Cheers kevin

You have a series of holes each side of the bracket on the transom 5 or 6 with a drop nose pin through the engine rests on that bar (trim bar) no 1 hole nearest the transom will make your bow dip no 6 will make it lift 2,3,4 & 5 are your adjustment between the max & minimum I run at no 2 or 3 mostly 2 so long as you set your boat up as it should be you will be ok

kevinsc · 04 June 2017, 18:40

Hi jeff
I see the trim hole on the clamp which is on the 2 hole will move it to the 3rd hole, over the next few weeks I am going to move the fuel tank ( which I thought was a 50l but is a 25l) to the front and put a battery next to it like your setup should make the weight distribution better.
Cheers kevin
[ATTACH]

jeffstevens763@g · 04 June 2017, 19:23

Quote:

Originally Posted by kevinsc

Hi jeff
I see the trim hole on the clamp which is on the 2 hole will move it to the 3rd hole, over the next few weeks I am going to move the fuel tank ( which I thought was a 50l but is a 25l) to the front and put a battery next to it like your setup should make the weight distribution better.
Cheers kevin
[ATTACH]

You will have to play with it Kevin no two boats, crew & equipment are the same what prop are you running you should have it stamped on one of the blades possibly a 10 1/4 x 11 inch?
Just reading again you started off ok so was you on the plane level and archiving a good speed if so your keel might have gone soft hence the floor creeking that will develop a convex hull air gets trapped underneath giving a banana effect and sluggish performance it can also give cavitation as the air passes the prop

kevinsc · 04 June 2017, 23:02

Hi jeff
It was fine at lower speed just on plane when I wanted to go faster thats when it felt strange dropped the speed and the boat went back to normal but didnt feel I was getting speed, checked keel pressure when got back and it was correct. Will have to have a play. Will also check the prop angle as Well.
Cheers kevin

kevinsc · 05 June 2017, 17:29

Hi jeff
I looked at my prop and its what you said but I noticed a small piece missing I don't know if this would affect it, what do you think
Cheers kevin

Mikefule · 05 June 2017, 17:48

I would say that is not useable long term, certainly not for a long run or at full speed. It is not just that a bit is missing, but that it is bent near to the break. The weight will be uneven because of the missing bit, and the water flow will also be uneven because of the bend and the ragged edge, meaning it will not work efficiently and it will vibrate which may in turn cause damage to bearings and gearbox. For comparison, think how much difference those tiny balancing weights make on the wheels of your car. Whether it can be straightened enough to be useable is beyond my experience, but you at least need to get it looked at and may need a new one.

jeffstevens763@g · 05 June 2017, 18:54

Quote:

Originally Posted by kevinsc

Hi jeff
I looked at my prop and its what you said but I noticed a small piece missing I don't know if this would affect it, what do you think
Cheers kevin

you need to get that nick sorted kevin or a new prop which is the way i would go since you are running a 13 inch pitch prop my guess is that you are only at 5000 rpm or there abouts at wide open throttle. if you go for a 10 1/4 x 11 you should get up to 5640-80 rpm at wide open throttle and the engine more responsive and faster.
is the ideal rpm range of that engine 5000 to 6000 rpm?if so the above will apply.
check my new boat thread for my testing with my 25 suzuki and you will see what i mean
i could go down to a 10 inch pitch which would put my rpm up to about 5800 rpm which i would do if i put more weight in the boat.
that could be your problem sorted think of it like a push bicycle too high geared [13 inch] hard to peddle [11 inch much easier]
Edit
Just googled the dt 25 but not sure of the Rev range your hand book should tell you.
You really need to know your wide open throttle rpm with your current prop and work from there.
It's not an exact science lots of factors in the mix.

kevinsc · 05 June 2017, 21:25

Hi all
I agree the prop looks bad and needs replaced but not sure when it happened. The full throttle speed is 4700-5300 according to the manual, I would like to get a bit more response out of it. I know I am new to this and need a bit of help so thank you for the help, I have had many jetskis in the past but fed up of the them so thought this would be better fun and I am able to take it on holiday with me and day trips to loch lomond.There is also a bit more to it than just jumping in and going for it.
Cheers kevin

kevinsc · 05 June 2017, 21:30

Also
Cheers kevin

jeffstevens763@g · 05 June 2017, 22:23

The way I would go is buy a tiny tach to see what rpm your doing now with the current prop then you will know what pitch prop you will need my guess is a 10 1/4 x 11

kevinsc · 05 June 2017, 22:57

Will have a look for tiny tach,do you know where the best place to get them
Cheers kevin

jeffstevens763@g · 06 June 2017, 07:42

Quote:

Originally Posted by kevinsc

Will have a look for tiny tach,do you know where the best place to get them
Cheers kevin

i got one from the same place as fenlander off ebay it was about £20 kevin.

one other thing i dought it has happened unless you have been unlucky just check to make sure your prop hasn't damaged the rubber bush when you hit something

Max... · 06 June 2017, 07:46

As he said - tiny tach and flat water with speed runs varying the height and trim of the engine each time is the only way to dial in the perfect set up.

If engine operating range is typically 5000 to 6000 then you want to be around 5750 at WOT ideally.

Check Loco's set up link a few posts into the 'Which SIB' sticky for the ideal guide to engine height/trim and set up.