Prop size and some other Q`s

[muzzytt]

Hi all firstly great site I have been reading a fair bit...

ok my question is I have a 5mt Glass runabout fitted with a I think 1995 100 hp johno it has gold/black engine cover.

its fitted with a 13-1/4 x 17 prop.. on wot I have seen 5100-5200 rpm pushing it to about 45 kmh on the boats speedo.

now all seems fine however I seem to get a lot of fuel usage. last week i managed to go through x 2 24 ltr tanks no sweat. I dont know if I am driving the boat wrong or maybe the engine needs a tune? or is this just normal.

I hae been coming to the thaught that I should go down in size with the prop hoping that will help a little with the economy.

2nd questio is I seem to be taking on more water as I noticed a lot of water coming out of the drain hole. is it easy to find leaks in a boat or is there a technique?

I am hoping to upgrade this boat next year to an aluminium boat like a TABS my mate has wich i was very impressed with. but need to fix these probs first.

thx for any input.

[muzzytt]

I also wanted to know I was given a johnson bilge pump with the boat however there doesnt seem to be any access to the bilge area of the boat am I thinking worng about this... as I wanted to be able to drain the excess water that accumalates were the drain plug is? I know this extra water in the bilge area is adding weight to the boat causing more fuel burn.

to give an idea of how much water is in there once I undo the plug there is a full tsream of water flowing for about 1 min to 2min before it fully drains.

time spent on water is usally 4-5 hrs.

[FNQCairns]

Muzz I think you should be seeing better performance from that engine on that hull with that prop, quite a bit better actually.

I guess the place to start is the leg height, rule of thumb is the faster you can get your boat performing at wot the higher the cruise speed you can obtain while still within the fuel efficient range of the engine.

Cruise speed is understood to be the most efficient speed both in time to destination and fuel use, this speed will be yours only.

One thing though, no V4 ever lasted very long at a wot of 5200, they last almost forever with a wot of 5750 though.

cheers fnq

[Spaniard_King]

Prove me wrong but that don't look like no V4 on the back there muz, sure it aint a 60 or 70 ???

[muzzytt]

thx for the input

I generally hae the revs at 3100 rpms the boat seems to plane at these revs I am yet to play with the trim settings as I dont exactly know what position is best.

when you say no 4 ever lasted much at 5200 rpm what do you mean exactly..are they more likely to fail at those rpms?... coming from a car racing background operating at higher rpms usually mean more wear an tear...

[muzzytt]

Gary the engine in the pic is a 50 hp johno that died when i baught the boat..;

so i ended up buying the 100 hp johnson V4

[muzzytt]

pics of the engine

[1975fflh]

I have a 90hp johno 1999 and the book says top RPM is 5200, I have a Coxcraft rumrunner 1989 5.2 metres and very heavy and it pulls 60klm at 5200 rpm that is usinga gps to measure the speed over ground, a speedo using a pitot tube measures water speed and can be inaccurate depending which way the water is running in a river.

[muzzytt]

also the engine is fitted with Lz hydro foils.

[FNQCairns]

Gary the engine in the pic is a 50 hp johno that died when i baught the boat..;

so i ended up buying the 100 hp johnson V4

Dunno for sure but it looks a bit like a 70s model V4 if so it would be rated at the powerhead so a fresh 85 or so HP at the prop but still lot's of torque compared to equivalent 3cyl more modern engines (except possibly the merc).

Very hard to get a boat setup with a foil, how close is the Vent plate to the bottom of the hull??

cheers fnq

[Spaniard_King]

fair enough Muz,

to me you have a 25 inch engine fitted to a 20 inch hull.. that prop looks way too deep IMO

[muzzytt]

Gary it is a 20 inch engine I baught it off tuncurry marine and that what he said .

probably the angle of the pic.

[muzzytt]

a proper pic of leg

I have removed the foils so its bck to how it was. I will test this next weekend.

from my research Im told the boat hull is a whiteline academy

[Spaniard_King]

Muz looks at least 2 inches too low, This will make a VARY big difference.

[FNQCairns]

Yeah I am with Gary, raise it till a little above the hull bottom like somewhere less than 10mm, it will make you happy:).

cheers fnq

[muzzytt]

so you guys say just raise it and leave prop alone for now?

[FNQCairns]

Yeah think so, your speed is by speedo so who knows how fast you are actually traveling. 5200 is too low to run that engine but it will go until it sticks the rings, catch's a port and snaps one, so any extra rpm you get will be nice.
Raising the engine and throwing the foil will get it traveling fast enough it can all come together and you should see 60kph (GPS) or more, if not, time to look a little deeper at the engine.

cheers fnq

[muzzytt]

I should have taken my tomtom with me that should still show speed while on water shouldnt it ?

anyway Ill see if i can lift the engine with current bolts otherwise I will have to re drill new holes.

interesting comment regarding the rings as I knew nothing of such a situation in two strokes.

anyone know what spark plug gaps should be on these motors?

[muzzytt]

any ideas on how i shoud solve this water in the bilge that seems more than usual?

[FNQCairns]

Yeah tom tom should work but I know bugger all about these things, culprit #1 for water intrusion is the engine mount bolts and also on a par is the bung/s, seal all of these like your life may depend on it.

Usually the standard holes drilled into the transom are enough to get the Vent plate above the bottom, with hope yours will be too.

yeah a V4 running 5200 will last longer than one running 4800 which will last longer than one running 4200 etc but one running say 5600 will last for ages in comparison, these particular engines can run 6000 all day long although no reason too, over 5500 while heavy will right the odds.

cheers fnq

cheers fnq

[muzzytt]

I dont think it would be engine mount bolts as the bottom bolts are on top of the bilge area and have not seen an wetness around that area. i actually drilled the transom holes for the bolts.

I mite try new bungs and see how we go. I checked the underside of the hull found some small chips and could see the fiberglass webbing along were the hull mounts the rubber rollers.

[muzzytt]

any other ideas on some of the other problems?

[1975fflh]

Do you tow tubes or people in and out of the boat or nets ets, you would be surprised at the amount of water dragged into the boat by these activities.

I have two bungs one for the deck and one for the inner hull, and I was getting quite a bit of water when travelling fast, but bugger all when fishing in the lake or outside.

What it was was a little hole about the diameter of a pen ink tube, it had been siliconed by a previous owner and only leaked whe going fast, a little fiberglass repair and no more water. ( I owned the boat for about two years before I found the hole.

Gordon

[muzzytt]

Gordon no mate I dont tow anything, the only things I have done is usual cruising and a little fishing and some wot blasts thats about all..

I want to also repair the chipped fiberglass whats best to use to fill these small chips in the bottom of the boat.

thanks

[1975fflh]

I just put a dab of resin with the hardener in a plastic cup and just paint on to seal the chip doesnt look great but if its not noticibale and not holed through it is just to seal. a repair kit with everything is about $20.00 at the local hardware store

[muzzytt]

here is a new pic of the allignment of the outboard I think if I raise it 2 inchs it should be enough?

[muzzytt]

I am also having trouble identifying the year model of the engine the serial numbers are G03031332

The model number is a SJWTPLS

hope that helps.

[Outsider1]

I am also having trouble identifying the year model of the engine the serial numbers are G03031332

The model number is a SJWTPLS

hope that helps.

Muzzytt,

here is a link to work out what the model number means;

http://www.maxrules.com/OMC_models.html

However the Model number you posted does not make sense to me. Normally the HP rating ie 100 is included in the number eg SJ100WTPLS.

And if you try to decipher the number you posted, the year model code does not work??


Got to fly.

Cheers

Dave

[muzzytt]

yep i was told same thing from a US source it seems to be a commercial engine ? thats what theye suggested.