1989 40hp tohatsu issue

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Also check the jack height. Typically, the anti-ventilation plate of the LU should be within 1 inch of the bottom of the boat. When at speed, the plate should ride slightly submerged. A motor that is too deep will drag more, making for a slower launch.

checked jack height and it was within ur specification.

moveing to the next hole up did help it would not plane at all even with weight up front.


I stumped maybe my setup is just too much for the lil 40

thanks

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Are you trying to plane a Titanic replica with your 40 ? Some issues to know :

Factory antiventilation plate heights parameters with respect to boat's keel is only reference, all boat's hull bottoms are not made same. You are probably dealing with leg drag issues. Is your boat spashing water sideways, is water entering boat through engine's sides ? Go for a wot test and do the following :

1-Trim your engine and test at 2-3 hole out transom as to have boat and AV plate parallel to water surface once on plane.

2-Ballance load/passenger up front.

3-Have a transom spotter check where is water flow passing with respect to tail, if passing above small plate will have splash issues and water drag that will slow your down, ideal flow must pass below small plate where triangle shape begins, by cuting water flow properly will achieve excellent performance on tight turns, best hole shot and best top speed.

4-If water flow is detected passing above small plate will need to rise transom accordingly, could place shims under swivel bracket to alter tail height if needed, test different shim heights untill water flow pases slightly under small plate. See pics for refference.

5-5500 rpm at wot is perfect, you only need to fine tune your set up.

By the way, what type, size is your boat and near weight ? Is it a flat bottom ?

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Hey i'm not sure on the weight but its a 14 ft fiberglass boat v hull .
I I will do the tests that you mention and get back to you

I thinking about trying smart tabs..

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Smart tabs are for planing faster and you already have a doel fin, if you got splash issues it's a motor/transom height thing, first check and shim for correct tail height acoordingly just for the test. Once combo is well fine tuned just distribute weight evenly. Should achieve a neat water flow at plane/wot as in picture..

My cousing bought this Boston Whaler with a 40C badly adjusted, excesive water splash at back transom as water flow was hitting the non triangular area, with a bit of patience rised the transom 2", realigned trim hole, moved console a bit forward, full engine maintenance and bingo, now boat is a real beast planing fast and scarry for one man driving at wot. Water flow is passing slightly under upper plate (yellow line) at wot. Pride owner has sideburn to sideburn smile after previous purchase frustration...

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

thank you for the picture it helps me understand your last post better.
the water definitely stays under the the upper plate and there is no water coming in from the sides of the engine.
I forgot to mention that the motor has a whale tail or dolfin thing attached to the cavitation plate.
without the fin the boat will not plane no matter where the weight is and the
max rpm it will achieve is 3400. I really like the tohatsu its not common here and seems easy to work on I don't want to re-power.
where can i find an explanation on how to properly shim?

 

[pvanv]

Re: 1989 40hp tohatsu issue

Also reduce prop pitch to get your rpm up where it belongs. A side benefit will be a better hole shot, faster planing.

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

No need to shim engine height if water flow is pasing slight under small upper plate at wot with anticav plate paralell to water surface, that's the ideal seting for best hole shot, nice boating and perfect tight turns at speed, if water flow passes let's say between upper and anticav plate, will have slight better top speed on a straight flat course, but will be awfull at thight turns and choppy water cruising, will experiment cavitation, aireation issues.

What don't understand is you mentioned having 5500 rpm at wot, how can you have 3400 now ? Probably you need a new prop, could be experimenting hub slip ? Go for the prop slip test to discard.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

No need to re shim engine height if water flow is pasing slight under small upper plate at wot with paralell boat to water surface, that's the ideal seting for best hole shot, nice boating and perfect tight turns at speed, if water flow passes let's say between upper and anticav plate, will have slight better top speed on a straight flat course, but will be awfull at thight turns and choppy water cruising, will experiment cavitation, aireation issues.

What don't understand is that you mentioned having 5500 rpm at wot, how can you have 3400 now ? Probably you need a new prop, could be experimenting hub slip ? Go for the prop slip test to discard.

Happy Boating

Doesnt really make sense to me either heres the breakdown
whaletail+people sitting on bow= 5500rpm

whaletail + no one on bow = 3400rpm

no whaletail + sitting on bow = 3400rpm

it only gets to 5500 rpm if the boat planes out..... if it doesnt plane the
rpm stay around 3400rpm..

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Seems you definitely have a spun hub, make this simple test. Remove prop from engine, mark 1 straight line or 2 separate points facing each other with red fingernail paint borrowed from your wife, let dry. Install on engine and go for a 1 minute wot ride. Remove prop, see if line is straight or points are still facing each other, if have moved during test, you have a spun hub. If the original prop was reaching 5500 at wot which is fantastic, I would stay with same size & pitch. Grease well shaft splines before reassembling new prop. The boat is not planing out fast because prop is loosing rpm/grip on the intent, it's like a car's clutch slipping when going up hill.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Seems you definitely have a spun hub, make this simple test. Remove prop from engine, mark 1 straight line or 2 separate points facing each other with red fingernail paint borrowed from your wife, let dry. Install on engine and go for a 1 minute wot ride. Remove prop again, see if line is straight or points are still facing each other, if have moved, you have a spun hub. If the original prop was reaching 5500 at wot which is fantastic, I would stay with same size & pitch. Grease well shaft splines before reassembling new prop. The boat is not planing out because prop is loosing rpm/grip on the intent, it's like a car's clutch slipping when going up hill.

Happy Boating

Great thank you for teaching me that test I will try it next chance i get
and report back. with a spun hub would people sitting on he bow
make a difference?
thank you

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Assume yes, with passenger at bow boat will have more hull lenght surface on water with less prop hub slip than with more weight at back, less hull surface on water and more hull drag while trying to break the inertia to plane the boat at wot.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Thank you very much for taking all this time to help me out sea rider .
I will post results If i can get out this weekend
thank you

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

I have marked the prop and hope to take the boat out tomorrow for testing .

I have been reading on spun hubs seems like it is more common the the rpm to keep going up with a spun
hub is it possibly for it to stay at around 3000 rm and still be a spun prop?

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Hard to tell, go wot with 3 passengers well distibuted and check marks. More weight more prop effort, you could have light or severe hub spun depending on load and rpm.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Thank you sea-rider,
Soon as I get a chance to test it I will report back I'm going to also get smart tabs seems like a lot of people like them .

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

You already have doel fins, with boat well ballanced and trimed, you don't need smart tabs. Before investing on them check prop condition, if it's the cause, buy a new prop and test as it is, then decide...

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

I check the prop and everything is still lined up so the prop and hub are fine.
I got my smart tabs and was able to plane out they also improved handling and
stability. The time to get on plane is still taking to long for me is there anything else
I can do to help the hole shot? how long do you think it should take for my boat to plane?

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

When you say it takes too long to plane, is it with you alone or with passengers ?
Are you still making 5500 rpm at wot, assume with just you alone ?
What's your top speed alone ?
Do you have a complete open 180? buttefly at full throttle ?
Is engine correctly height seated on transom ?
Are you still using doel fins + smart tabs at same time ?
If so, remove dole fins and test with smart tabs alone.
Mine being a light rib/engine combo planes in 3.5 seconds.


Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Yes rpm are still about the same sounds like i'm expecting to much from my setup takes me about 8-10 seconds . I am not using doel fin just tabs. With my wife it planes every time but if i take a male friend I guess the weight is to much and it doesn't plane every time.
my max speed is only 25 mph according to gps.

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

8-10 seconds is not a lifetime, but is long and frustrating.
Better take a female than a male friend ha,ha.
Does your boat have a special hull design of some type ? Or it's a real heavy lump ?
If GPS is reading right. 25 MPH is definitely poor, my 18 does tad less than 22 MPH.
Have you 180? throttle butterfly at full wot and magneto plate mark reaches/stops at 25? ?
Know how to check ?

Happy Boating