Increase horsepower on Zodiac

[joe_classic]

Hi all, soem of the other members are helping me with purchase of a 40HP 3 cyl Tohatsu but I had not mentioned why I was repowering.

Heres the drum - I currently have a 30HP 2008 2 stroke Tohatsu on a Zodiac (Alum floor) Mk2C (3.8 metre) Futura Hull with forward controls and a light seat and steering frame.

I am having trouble with the boat reaching quick planning with 2 up failrly heavy crew at 90kg each - no we can't loose weight just now) If I add a bimini top with light winds the situation is hopeless.

Boat is rated for max 40HP and 95kg engine weight so the Tohatsu just gets in at about 87kg. With the 30HP I have tried one prop pitch down from standard, changed weight distribution, motor heights and trim but it still struggles. Most noticeably it dies in tight turns. BTW - I had this Tohatsu from new so don't suspect engine problems.

I am thinking of repowering with a 40HP Tohatsu 3 cyl (40D). I suspect the 30HP is OK once she is spinning fast and on plane but because of its relatively small block I suspect it just doesn't have the torque and block size for easy hole shot and am guessing the 40D with around 700 cc block size should substantially help. I previously had a 1995 25HP evinrude which had much better hole shot.

Does anyone have experince with this boat and a 4oHP Tohatsu or other. The other problem is the transom is for short shaft and the secand hand motor is 20 inch Long shaft. The next Zodiac up (Mk2 4.2m) has a long shaft spec and the transom appears to be identivcalk except does not have a deep cutout as my boat has on the transom. I can easily biuld up the transom by filling in what Zodia cut out of my transom.

The other advantage is I get elec trim and tilt on the 40HP meaning I never have tpo leave my seat on launcg or to correct trim.

Any thoughts on this whole madness of mine.

Thanks again for your answers

 

[jondavies]

Re: Increase horsepower on Zodiac

Hi all, soem of the other members are helping me with purchase of a 40HP 3 cyl Tohatsu but I had not mentioned why I was repowering.

Heres the drum - I currently have a 30HP 2008 2 stroke Tohatsu on a Zodiac (Alum floor) Mk2C (3.8 metre) Futura Hull with forward controls and a light seat and steering frame.

I am having trouble with the boat reaching quick planning with 2 up failrly heavy crew at 90kg each - no we can't loose weight just now) If I add a bimini top with light winds the situation is hopeless.

Boat is rated for max 40HP and 95kg engine weight so the Tohatsu just gets in at about 87kg. With the 30HP I have tried one prop pitch down from standard, changed weight distribution, motor heights and trim but it still struggles. Most noticeably it dies in tight turns. BTW - I had this Tohatsu from new so don't suspect engine problems.

I am thinking of repowering with a 40HP Tohatsu 3 cyl (40D). I suspect the 30HP is OK once she is spinning fast and on plane but because of its relatively small block I suspect it just doesn't have the torque and block size for easy hole shot and am guessing the 40D with around 700 cc block size should substantially help. I previously had a 1995 25HP evinrude which had much better hole shot.

Does anyone have experince with this boat and a 4oHP Tohatsu or other. The other problem is the transom is for short shaft and the secand hand motor is 20 inch Long shaft. The next Zodiac up (Mk2 4.2m) has a long shaft spec and the transom appears to be identivcalk except does not have a deep cutout as my boat has on the transom. I can easily biuld up the transom by filling in what Zodia cut out of my transom.

The other advantage is I get elec trim and tilt on the 40HP meaning I never have tpo leave my seat on launcg or to correct trim.

Any thoughts on this whole madness of mine.

Thanks again for your answers

Have you thought about Smart Tabs? A lot of inflatable owners swear by them. They are a lot cheaper ($100US) than a new motor and a lot less hassle than building up the transom.

I tried them on my boat and they worked a little too well -- even on the lowest setting, they provided so much lift at the stern that I was getting cavitation/aeration.

The manufacturer is very accessible and helpful -- you should call them to see what they recommend.

 

[nobrainsd]

Re: Increase horsepower on Zodiac

Interesting post. I own a mk2 Futura. I never had much problem getting up on a plane. Excessive bow rise on hole shots was my biggest issue. I do have a Nissan 40d 3 cylinder on my boat. It seems to me that you have more than one issue to address. First off, a long leg outboard on a short transom boat will induce a lot of drag. Changing the transom or the outboard will make a big difference. Where is the weight in the boat? I had to move my battery and gas tank forward to get better hole shot performance. I also have my seats as far forward as I could go with the console bench right up front on the aluminum floor section. Weight distribution is very important. I also run with smart tabs. I do hear what sounds like a little air being drawn down into the prop occasionally, but the performance advantage of the tabs is really big and definitely makes a huge difference on hole shot starts. I also have an adjustable 4 bladed pro pulse prop. I was surprised at how much I had to change the pitch to get the proper rpm at full throttle under load. The right prop makes a difference too! Your Mk2c with a 40d should jump onto a plane.

My top end speed is only around 28 to 29 mph. I have two suspension seats installed and they add a lot of weight. Unless you run really light it is hard to get a lot more top end speed. The zodiac hull creates to much drag as the boat goes faster. Certainly not as efficient as a hard hull or rib.

When you say your outboard dies in tight turns are you actually meaning that it shuts down? I would guess not or you would be looking at the outboard as an issue. Tight turns will scrub off speed, but I do donuts at full throttle and I have to be careful not to launch sideways off my wake.

A Futura is certainly not a ski boat, but you should be able to get it to jump and go if that is what you want it to do. My Futura took me about 70 miles out on Lake Powell up to the San Juan arm and we had a great time hydrofoiling behind it there. A little slow on starts, but two heavyweight riders and a foiler got up on a plane after a little hesitation and easily hit 22 to 24 at 5000 rpm with a little more throttle to go. In addition to the suspension seats, two big guys and a towed foiler I was still carrying something like 16 gallons out of my 22 gallons of gas on board when the photo was taken. I get 22 - 24 at around 4700 - 4800 rpm normally. My 40d is a 98 and I'm sure the compression is getting a little low. This should give you some idea of what you can achieve.

 

[Sea Rider]

Re: Increase horsepower on Zodiac

That sib with just 2 mates weighting 90 Kg each should plane fast, you should check :

-Sib tubes and keel are correctly top air inflated Min 3.0, Max 3.5 psi
-Engine sits on transom perpendicular to water level (adjust trim angle if needed)
-Load is evenly distrubuted inside deck.
-No water splashes at back transom or splash coming inside deck.
-Engine is 100 operational and well timing advanced (25? deg) at wot.
-Current prop is 100% operational and not begining to have small hub spun issues.

What does dies at tight turns means ? You are experimenting cavitation, aireation issues, if so, engine sits to high on transom.

Check with Tiny Tach, Hardline induction type tachs max wot rpm with load (passengers) you are currently testing with. Probably you are under proped for that load, a tach check will crarify. Other good alternative Tohatsu 2 stroke 40 C, 2 cylinder, slight heavier and with 500 CC punch.

Happy Boating

 

[joe_classic]

Re: Increase horsepower on Zodiac

Thanks guys - great responses.

Nobrainsd - I'm sure your picture would have been good but I could not see the boat in the photo - not sure if something wrong at my end - can only see the mountain backdrop so would like to see the whole photo or was it a movie ??

I'm also concerned with the 40D adding to much weight or stressing the transom to much even though Zodiac claim max 95kg is permissible - have you had any trouble with excessive transom weight or stress on the transom fixing to the tubes - the Mk2 transom really seems to look exactly like the Mk2C except the manufacturer produced my short shaft transom with two cut downs instead of the one cutdown that the Mk2 has so I'm thinking I should be able to build up the transom for the long shaft. Problem is you cant get or is very hard to get a short shaft 2 stroke 40HP that is power trim/tilt hence why I need to go long shaft and mod my transom. BTW my Mk2C is a 2008 hull so has the larger 550mm tubes ostensibly to support 4 stroke motors according to Zodiac.

to "jondavies" thanks for your input on the trimtabs I will certainly look into that as wel. I had hydrofoil fins on my evinrude maybe that made the difference but the local Tohatsu dealer scared me off putting fins on the motor saying I would void the warranty if I drilled into the motor plate to put on the fins so I haven't tried that. Its out of warranty now so whatever. I'm not sure if smart tabs are the same I'm about to check out your link now to see them.

The last thing is my Zodiac gives a pretty rough ride on chop udestantable due to hull - I may be better selling my hole rig and goes to a RIB and getting back speed and performance through the better hull concept. Mine is a trailer boat anyway so never deflate.

Anyways good to have the discussion - any further input always appreciated. ... great forum this one - cheers

 

[henryfreston]

Re: Increase horsepower on Zodiac

I have a 25hp tohatsu on a 4m honwave. I have found that when pulling off fast (accelerating) I get a lot of cavitation. I am going to try the doel fins on mine and see if it is any better. I am upgrading the outboard to a 30, what speed should I expect with a light load (no more than 120kg).

Henry

 

[joe_classic]

Re: Increase horsepower on Zodiac

Apogies to all for my long posts

Thanks Sea Rider just missed your resonse whilst writing my latest reply.

Tubes are fully inflated and have tried various Trim setting - usually I go with number 3 hole on the Tohatsu not sure if that ends a perpenicular but does stop purpoising on smooth water and seems best overall for steering drag etc.

I'm not sure about the engine timing - The engine is relatively new and even from brand new had the problem but I should check this - not sure how to do on a boat motor know easily how to do on a car engine - on the Toahatsu don't know where to start - wheres the timing mark - which piston to attach timing light and how to adjust anyway and at which revs are we looking at the 25 degrees.

Re Tiny Tach I do have one but reading is erratic after I extended the lead - I need to speak to tiny tach about that - I extended the coax correctly with the right type of coax and have changed the turns around the plug every which way as well as tried different earth attachments and still no luck so that is hopeless at the moment - I would rather an analog tach to tell you the truth but don't know where to source for that motor and where to connect - info seems to be sadly lacking on the web re this stuff - at least when I look for it. The forum seems to be the way to go - should have asked earleier as have learnt much in the last two days.

I'm not sure what you mean by hub spun - I assume you are saying that the prop is spinning on its rubber fixing but prop is quite new so doubt this and i think I would have felt something.

There are water splashes at back transom so maybe motor is still to low on the transom - I need to check this.

Re loading - this is always a hard one - all I can see is I always seem to be struggling to get on the plane for one reason or the other even though Zodiac claim 30hp should be fine and the forum seems to think so as well - I;m reasonable experinced with these boats but I am a bit stumped - its just feels like this motor does not have enough cubic inches to get the torque of lets say my old evinruce 25HP which was larger block capacity but only 25HP.

Trim tabs or fins could be the answer.

Many thanks again - BTW great location I noticed your from "Lima-Peru" wow !!!

 

[TOHATSU GURU]

Re: Increase horsepower on Zodiac

Sick engine, wrong prop pitch, incorrectly loaded boat, incorrectly inflated boat or bad karma. Take your pick....You can't use a long shaft engine on a short shaft boat and expect ANY performance.

 

[Sea Rider]

Re: Increase horsepower on Zodiac

Is that a 2 strokes engine ? if so which model ? can pass it to 30 HP for peanuts if 2 strokes. You must not have splashing issues at back transom as this craetes more tail drag and lessens sib/engine performance. If possible buy the latest standard TT 2A hour/tach model : http://tinytach.com/gasoline.php Set it to fire at 360?

Have a TT myself but it's the older model which reads double when used on 2 strokes engines, if possible to get where you are located, go for one. Measure the height from upper transom to lower keel, what's the distance ?

Meanwhile with engine perpendicular try placing a 1" wooden shim at upper transom, go for a spin and test different small shims heights untill water splashes dissapears to start with, then we can go along fine tuning that combo to work as expected. Ideal water flow at plane must pass slightly under small upper plate as shown in video. Tohatsu are natural water splashers if not correctly height transom seated.

This might help to understand better : http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be

Happy Boating

 

[joe_classic]

Re: Increase horsepower on Zodiac

Hi Elvin,

sure I understand about the long shaft - I was going to modify the transom to lift the long shaft - Zodiac for some reason made an enormous cut out on the transom to allow for a short shaft. As far as I can see it is the same transom as on a Zodiac Mk2 4.2 metre boat but with 2 levels of cut down on the transom to alow for short shaft - I was not going to just throw the Lshaft onto unmodified transom but would basically fill in the cutout to lift the mounting point - maybe they had other reasons for s-shaft but not sure what.

Given this do you still disagree with the Long shaft - weight is actally more my concern right now and the different leverage the Lshaft will present to the boat. The weight of 87kg for the 40d fits within the Zodiac 95kg max engine weight spec. Agreed if I use trim tabs and get the motor correctly setup maybe 30HP is quite sufficient at 50kg it is quite a bit lighter.

As far as engine goes it really should not be sick unless I was sold a brand-new lemon. It sounds fine - timing could be out as I have not tested that - if it is out then it left pre-delivery that way.

I desperatly want to get a tach on there that is reliable then I can look further into prop pitch but as mentioned already dropped one size to try and improve hole-shot.

These SIBS are natorious for bow rise and yes agreed they are weight distribution sensitive.

Thanks for all your very valid points - I am working through them again - need to get back on the water.

If you have any pointers on fitting the tach to this electric start Tohatsu that would be good - the local distributor is less than helpful and given the right info I'm sure I can fit a decent analog tach. The engine model is a M30A4 346B

 

[joe_classic]

Re: Increase horsepower on Zodiac

Also Sea Rider per my other post the engine is an M30A4 346B 2008 2 stroke 2 cylinder forward control electric start. Not sure if you were replying to me oir "henryfreston".

My TT tach was the commercial gasoline model about 2 years old.

Height from top of transom to lower keel is exactly 15 inch but the boat rides higher than would be expected when on full plane as it tends to ride higher on the speed tubes. I have also spaced the engine higher on the transom by 3/4 inch.

 

[Sea Rider]

Re: Increase horsepower on Zodiac

Some issues to bear in mind to fine tune a sib/engine combo,

When you say tubes are fully inflated is that with a pressure gauge ? If not, fully does not means rigid as needed, probably way under infalted. Start with correct pressure min 3.0, max 3.5 psi once sib once sib is floating for a while for pressure to staibilize, top if needed. Zodiac sells pressure gauges.

If under inflated sib has much more water drag and if with water splashes at rear transom worst. Is it possible to add some pics of the transom area ? You are using a short shaft engine mounted on a modified transom intended for a long shaft engine ?

Changing a less pitch is a wild guess, you must do it once sib is inflated to it's working pressure and engine is well trimed & transom height seated, that is with no water splashes at transom rear whatsoever. Then with tach, with well ballanced sib go for a wot spin and check if inside min, max working rpm parameters stated for that engine, if possible test on flat calm sea.

Happy Boating

 

[joe_classic]

Re: Increase horsepower on Zodiac

Thanks Sea Rider.

JUST TO CLARIFY - At the mpoment the boat has a 30HP S-shaft and the transom is not modified and is still as standard (ie 15 inch transom. I probably confused the picture because I am considering buying a 40HP Tohatsu L-shaft and fitting this to alleviate my problems. To fit that motor I will need to modify the transom to allow for the L-shaft of 20 inches so I would fill in the significant factory cutdown in the existing standard transom. I can easily gain 5 inches by installation of a plate to fill in the existing factory cutdown in the transom. The penalty is a much heavier engine - I would be going from 50kg to 88 kg engine to gain the torque of the 700cc 40HP tohatsu 40D. My dilemna is to go the 40HP route whilst I can still purchase this second hand motor or continue to fiddle with trim tabs, smart tabs, dolphin fins etc to fix my current problem. In the meantime I may miss the opportunity to purchase the 40D motor which in Australia comes up rarely.

In short I need to take the plunge and assume the extra power (albeit also extra weight) may fix or miss the deal on the 40hp and try all manner of other things to fix the 30HP. I will never know if the 30HP was just a matter of underpower.

Hope that clarifies and thanks for your help. I will try and post PICs but that will take a little.

 

[henryfreston]

Re: Increase horsepower on Zodiac

Thanks Sea Rider.

JUST TO CLARIFY - At the mpoment the boat has a 30HP S-shaft and the transom is not modified and is still as standard (ie 15 inch transom. I probably confused the picture because I am considering buying a 40HP Tohatsu L-shaft and fitting this to alleviate my problems. To fit that motor I will need to modify the transom to allow for the L-shaft of 20 inches so I would fill in the significant factory cutdown in the existing standard transom. I can easily gain 5 inches by installation of a plate to fill in the existing factory cutdown in the transom. The penalty is a much heavier engine - I would be going from 50kg to 88 kg engine to gain the torque of the 700cc 40HP tohatsu 40D. My dilemna is to go the 40HP route whilst I can still purchase this second hand motor or continue to fiddle with trim tabs, smart tabs, dolphin fins etc to fix my current problem. In the meantime I may miss the opportunity to purchase the 40D motor which in Australia comes up rarely.

In short I need to take the plunge and assume the extra power (albeit also extra weight) may fix or miss the deal on the 40hp and try all manner of other things to fix the 30HP. I will never know if the 30HP was just a matter of underpower.

Hope that clarifies and thanks for your help. I will try and post PICs but that will take a little.

If you are going for torque why not go for a 4 stroke?

 

[joe_classic]

Re: Increase horsepower on Zodiac

If you are going for torque why not go for a 4 stroke?

Hi Henry - ah the 4 stroke - that might be great but again controversy about what has more holeshot 2 stroke or 4 stroke. I would have thought 4 stroke has more torque and to me that means more holeshot but I'm no expert.

The other thing the 40d 2 stroke is available to me second hand - I believe it is lighter than a 40HP 4 stroke and certainly cheaper. If money were no object you could just keep changing but you would have to awfully rich to play that game.

In my experience getting the right motor for these Zodiacs is always a problem. Zodiac, at least in Australia, (and their retailers) have never given much help - they just sell the boat and leave motor selection up to you or the dealers will sell what ever motor they like to push.

The engine manufacturers rarely show application charts for their engines on smaller Zodiacs like they do on more popular solid hull craft, I have found the only way, is from personal experince of others, that you can hope to even come close to a proper engine selection.

Then you are legally limited to 40HP on this boat even though that puts you in the weight range of a 50HP but legally(insurance) you can't fit a 50 - then Zodiac decided to make this a 15 inch transom reducing your options again - few 2 stroke short shaft engines have power trim tilt - 4 strokes do but they are heavy for a light inflatable.

Anyway I just know how to make a short story long

 

[TOHATSU GURU]

Re: Increase horsepower on Zodiac

You have to modify the transom or modify the engine. No choice other than those two. One is not better than the other, so go either route. The tach need to be the Tohatsu tach or you may wind up with spurious signals. Aftermarket tachs usually cannot handle the ignition pulse correctly so you can wind up with odd, inaccurate RPM readings. The 2008 is now 5 years old and should not be considered new unless it has been in service less than 3 months. Having said that, the timing cannot change unless someone screws with it and they are correctly timed from the factory. So, you have to pick some aspect of your boat/engine combination and start either the trial and error or book diagnostic process.

Side note: Torque is not important as a measurement by itself. The gear ratio is fixed as you cannot shift from one ratio to another so an engine that might have great "torque" at X RPM sucks the big one at another RPM. Hence the reason that outboards are measured at PSH or prop shaft horsepower where the last measurement can be taken...Still an issue due to prop slip, but at least you weed out the other meaningless measurements along the way.

 

[Sea Rider]

Re: Increase horsepower on Zodiac

If wanting to keep 30 HP and perform well, you need to place minimum a wooden 1/2" shim on transom to raise it to 15.5" or 40 cm transom height, go for a wot spin, if still with slight water splashes, increment more shim height to first 1/2" shim untill you see no water splashes at back transom. Before buying a larger engine, check tube's pressure, trim angle, transom height and max rpm with an induction Tiny Tach.

Happy Boating

 

[joe_classic]

Re: Increase horsepower on Zodiac

Thanks sea rider. I already have raised the 30 hp by 3/4 inch with a shim. Tube pressures are correct at 3.5 psi. The only thing i can think is trim tabs or smart tabs. Also i should probably move my set forward maybe to much rear weight.

Im a little worried putting on the 40hp duE to the weight. It would be really good if someone could confirm that the 30 hp should really do the job on this boat and that would only be known by someone with a mk2c that is running a 30 hp tohatsu.

Sea rider what is your boat ans what engine - i notice in your avatar you are running a thatsu dont know what power and what boat.

Also whats the forum thoughts on smart tabs or dolphin fins for my problem.

 

[Sea Rider]

Re: Increase horsepower on Zodiac

Joe,

See it this way, if your sib is rated for a 40 HP engine will gladly take on plane it's full passenger capacity rated at tech plate, if you will be boating alone, with fianceee, teenagers 70% of it's max rated power will do the job. What is your set ? you have a central console/seat or it's a open sib. If it's a open sib, place a mate at bow and go for a wot spin, with you sitting on deck visually check water flow, ideal flow must pass slightly under small upper plate with engine trimed perpendicular to water level.

If still with splashes must raise shim accordingly untill water flow at tail is near smooth, probably you still have water flow hitting the non triangle area at lower tail.

I ran a 420 sib with just a Tohatsu 18 HP on a rib rated for minumum 30 HP, no trim tabs, fins whatsoever. The rib is so well engine, transom tuned that don't neeed to even place myself an inch forward from tiller to be on plane in 3 seconds. So, if an 18 HP can wot nicely at 40 Km/H on a rib that weights more than your sib, can't understand why you are unsatisfied with the 30 HP performance. If same engine is placed on my rib will achieve 65 Km/H on flat calm waters. Check if your 30 HP is achieving full opened butterfly (180?) at wot ?

Once you have engine sitting correctly on trasnom, etc, place an induction TT and go for a wot spin, check if inside min 5150, max 5850 rpm parameters at wot, you could be underproped, that we don't know and a TT will definitely tell you. Some boaters swears by trim tabs, doel fins can be garbage collectors, before investing on trim tabs, move your weight forward and test. Post results. To have some idea about fine tuning sib/rib check pics.

Happy Boating

 

[fbpooler]

Re: Increase horsepower on Zodiac

Don't mean to be the wet blanket, but the difference between 30 and 40 HP is not great if the 30 will plane a boat. It is also a guess to compare a RIB to a SIB performance wise.

I would look at tabs and prop selection before changing motors, making sure the RPM was in range for the motor. Transom weight differences can be brutal also, so the four stroke may dissapoint you.

As far as 2 stroke vs 4 stroke, back in the day Yamaha came out with a 350 cc 2 stroke racing motorcycle and ran them against 4 stroke 500 cc motors. They ate the 500 cc motors, and I believe they had to have a rule change to make it fair.

Remember that a 2 stroke fires each time a piston approaches top dead center while a 4 stroke cylinder fires every other stroke. Prop HP is what you are looking for with either design. Then make sure either is operating at rated RPM. You could drive yourself nuts trying to compair without testing. Long stroke, short stroke, prop design, boat drag, weight distribution, etc. You also cannot compare two hulls of different design or construction.

Hope you get this sorted out with the least expence.