any thoughts

I own a formosa center cab (walk around) 550.the boat has a 4mm plate hull with a 15deg dead rise, overall length is 5.65m, beam 2.40m, weight 620kg, floor to gunwale 700mmx3mm, has a 150ltr under floor tank and is registerd to carry 6 people + gear + motor to the weight of 775kg = combined weight of1395kg + fuel.I carry a 80ltr esky with ice for fish.It is powered by a m140hp tohatsu 2stroke which is mounted on a pod. this boat and motor is only 12months old bought brand new. Has only 30hrs on the clock. It is using up to 40%+ more fuel than a blue band 2stroke mercury. my prop is 13.25"x17"p same as the 100hp merc. on a 19ft fiberglass half cab carrying more weight. should i go bigger in the prop or could it possible be tuning. the motor will rev to 5800+ at WOT. coming up out of the hole it struggles when fully loaded and has trouble holding up on plane when you just want to cruise. seems like you have to travel flat out all the time. I am tending to think I should go less piitch or smaller prop, so as to help at lower revs.
any thoughts
bill

Re: any thoughts

I do not have any experience with bigger boats or commercial boats, but it sounds to me like you are under powered. You compare it to another boat with mercury power but don't mention how much. An engine which must run flat out to power a boat will of course use maximum fuel. Prop positioning both vertical and distance from the stern will make a difference in performance, perhaps some pictures would be of assistance. I hope this gives you some ideas. Randy

Re: any thoughts

the hp on the merc. is 100hp. the max for my boat is 140. could i be under propted. I dont know how to put up picture

Re: any thoughts

Your boat/motor only being 12 months old shouldn't have the typical faults, reasons some older boats get like water logged flooring, foam but is the boat covered at all times when not in use? Do you ever find excessive amounts of water in the bildge? Is the motor in good tune? Have you checked your spark plugs? They can go south even when they are brand new, are all your plug caps tight on the plugs and coils? Any chance of bad gas or plugged gas filter?
Look at the obvious things first and if all checks out then a return trip to the dealer for some warranty work(provided you still have warranty?)........Irv964

Re: any thoughts

What is your speed at max rpm?Can you give us the size and weight in sae demensions?The motor must be at its max reccomended rpm now isn't it?
I think I would start with the setup.vertical height in particular.
If you have no ventilation trouble you are probably not high enough.
raise the motor a hole at a time to a point just before venting becomes a problem.Be sure it pumps water.Some live with occasional venting to achieve max height.An inch could add a couple of mph.You might want to try some trim tabs perhaps something like smart tabs.There are also props that can improve hole shot and speed.Generally an increase in pitch will ruin what little hole shot you have.It will be interesting to see your speed at max rpm.(GPS speed is best)

Re: any thoughts

thanks for your thoughts.
best speed by gps that I have saved is 60kph with 3 people gear and full fuel at wot.

Re: any thoughts

Lets see if my math is correct thats over 3000 lbs I would think the 140 would have trouble planing at max weight.With motor on a pod you have over 400 lbs hanging a couple of feet behind the boat,not counting the weight of the pod.Over 10% of the total weight. Where is the gas tank,battery etc? I think 60km converts to about 37 mph a respectable speed.So the motor is capable.I think trim tabs will get you out of the hole better and keep on plane at reduced power. There are also props that give stern lift but I think tabs do an overall better job for less money especially smart tabs.
I couldn't find the actual weight of a 140.Do you know it?

Re: any thoughts

hi your sums are right, and the tank is right behind the seats running port to starboard. the motor weighs about 164kg(361,1/2pounds). I was told not to put tabs on by salesman and the tohatsu dealer, why I dont know. I think i am going to try a smaller prop in dia. or less pitch and see what happens. and try to find out why they dont want me use tabs. Bill

Re: any thoughts

Does behind the seats put it in the rear part of the boat?
If you can't use tabs you need low end help. A 4 blade prop helps low end performance and may help stay on plane better.A stainless prop may do it even better. A smaller/less pitch prop may help your hole shot but your all ready over reving or damn close to it and I think your fuel use will be worse.
Your 100 hp merc would use about 10 gph(gallons per hour) at wot.The 140 about 14 gph. Thats about 40% more.I've got to say again without tabs a 4 blade is the way to go.

Re: any thoughts

With the pod trim tabs are going to put a lot of force into the pod, maybe that is the reason they are not recommended. Nice boat. I would also think that a 4 blade prop would be part of the answer. You are pushing a ton and a half fully loaded and that is why I commented on bigger boats,commercial boats before. Best guess here would be stick with the 13 x 17 in a 4 blade or drop to 13 x 15 4 blade stainless. Either one will get you out of the hole better and push that weight with all the power you have.

Re: any thoughts

hey guys thanks very much for the input into my problem. by the end of october I hope to have it sorted out and I will let you know which way I went. answer to where tank is, it is vertualy right behind cab.
bill

Re: any thoughts

hi in your reply you say I should use a 13x7 4blade prop, is that actual size or is it 13.25x17 that is stay with the same diameter.
bill

Re: any thoughts

http://boatpropellers.iboats.com/Tohatsu/140_HP_(1988-and-Newer)_15.00-Pitch_Propellers/337/?rotation=Standard&**********=905244464&*******=958634535


3453-133-15
13-1/4?
15?
4
Standard
Not Available
Not Available
Hub Unavailable



That is the prop...along with some nauticaus trim tab's ..a whole new boat...Opps then there is motor height and a set back plate..But thats for the O/B pros..........

Re: any thoughts

Sorry I did not look in the charts before typing that post. You will find that each pitch for a given application has a diameter which the manufactures attach to it. Sizes range from about 12 1/2 to 13 3/4 , I just casually called the range 13" Looking in the chart I see as Tail Gunner posted there is not a 15" pitch 4 blade stainless. Darn the bad luck. In that case my guess is with the 13 1/4 x 17. There are prop exchange programs out there see if you can take advantage of one to try it out and if not exchange for what WOT throttle and hole shot tell you that you need.