Prop blowing out

patcarr1992

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Nov 11, 2017
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1
I have a 1752 custom welded flatbottom. I have a bowfishing deck on the front, center center console and 2 pods on the back added. Installed a 2007 Yamaha 2 stroke 70hp with 13.75x 15 prop.

Holeshot is great, all the way up to 3/4 throttle. After that any more throttle causes it to plow. I try to trim out and prop blows out and rpms jump past 6k. Only getting 26 mph when plowing. Any suggestions?
 

QBhoy

Fleet Admiral
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Mar 10, 2016
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8,286
Not an expert on this type of set up...someone who can advise better will be along shortly, but I?d say it?s likely to do with it being flat bottomed and the engine height set up.
What are the two pods you refer to ? Excuse the ignorance. These kind of boats aren?t common over here.
 

Fed

Commander
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Apr 1, 2010
Messages
2,457
Sounds like the bottom is hooked, look for a concave area on the bottom of the hull.
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
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Being a 10 year oldie prop will firstly check if prop is in a healthy operational state, perform a prop slip test to rule that out.

If boat's bottom is hooked can't modified that, was factory built that way and will need to live with it if plan keeping the boat for some time. If with manual trim trim OB to sit at 90? on transom, distribute deck weigh evenly, go for a wot spin on flat calm water cond and check if lower leg produces back or over transom water splashes or if prop aerates on straight water courses.

If splashes will need to raise OB till splashes are cancelled out, if with prop aeration will need to chop transom down till prop doesn't aerate, can trim OB to better the situation, but prop will lose its best thrust.

Happy Boating
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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47,297
My guess the pods are lifting the stern. Couple that. With a stern lifting prop any you have blow out.

Try a bow lifting prop. If that doesnt work, move some of your weight from the bow to stern.

If that doesnt work, loose the pods
 

ahicks

Captain
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Sep 16, 2013
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3,957
Agree with Scott. Time to get a long straight edge under that boat to see if you haven't got something going on there. Could be the pods were installed improperly, or a weak area of the bottom ahead of the transom that needs to be reinforced. If you do find an issue, thankfully custom alum. builders aren't too hard to find, and they should be able to suggest what action needs to be taken.
 

Stumpalump

Chief Petty Officer
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Dec 5, 2013
Messages
413
Just drop the engine height. Pods may be holding your bow down and you need more trim to get the bow up. Lower the height so you can trim up more. If that's not possible then make a hydro fin out of aluminum plate. Give it a bend to force the bow up under way and you will still have all of the low speed benifits of the pods. Let it be a lesson to others that think they need pods. They have their pros like stern floatation while fishing and cons like performance and are deadly in a following sea.
For you glass guys pods on a tin boat are floatation boxes welded to the transom suposidly to add lift in shallow water and to add stability to overloaded small boats. They do as much harm as good but as you know with boats everything is a trade off.
 

jimmbo

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May 24, 2004
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For you glass guys pods on a tin boat are floatation boxes welded to the transom suposidly to add lift in shallow water and to add stability to overloaded small boats. They do as much harm as good but as you know with boats everything is a trade off.

???? Picture please
How would a 'pod' hold the bow down? The extra weight hanging on the transom should raise the bow.

As for adding a hydro fin to force the bow up... ????? If you mean something like those god awful things that bolt to the AV plate, the rear of the AV plate is the first thing to be clear of the water when the engine is trimmed up. By dropping the engine to ensure it would be under water is going to create all sorts of less than safe handling issues
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
I have a 1752 custom welded flatbottom. I have a bowfishing deck on the front, center center console and 2 pods on the back added. Installed a 2007 Yamaha 2 stroke 70hp with 13.75x 15 prop.

Holeshot is great, all the way up to 3/4 throttle. After that any more throttle causes it to plow. I try to trim out and prop blows out and rpms jump past 6k. Only getting 26 mph when plowing. Any suggestions?

Is the bottom truly flat? Or does it have a rib running down the centerline that sticks out an inch or so below the bottom of the hull? If so then the engine AV plate would have to be below that rib.

Pictures, good ones, would help a lot
 

Stumpalump

Chief Petty Officer
Joined
Dec 5, 2013
Messages
413
???? Picture please
How would a 'pod' hold the bow down? The extra weight hanging on the transom should raise the bow.

As for adding a hydro fin to force the bow up... ????? If you mean something like those god awful things that bolt to the AV plate, the rear of the AV plate is the first thing to be clear of the water when the engine is trimmed up. By dropping the engine to ensure it would be under water is going to create all sorts of less than safe handling issues

https://www.explorebeavertail.com/product/flotation-pods-large/

They act as trim tabs and can force the bow down. An AV plate works like magic if you use sense, make your own and stay away from the plastic batman contraptions. A little angle up or down can raise or lower the stern while under way and that effects the bow. Dropping the motor if it's too high allows you to trim higher without ventilation. Everybody especially flats boat want the engine as high as possible. At some point you loose the ability to trim up. Suprised a guy with 5000 posts would ask unless you have not seen these pods. I don't like them because at least half of them add more problems than they solve. Now when sombody steals my previously posted idea to mount them on a Bennett trim tab actuator that opinion may change.
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
I have never seen such things. I guess they would function as an afterplane. Afterplanes do help with stern heavy boats, but would certainly render any amount of positive trim ineffective and thereby increase the chances of blowout. A fin to increase positive trim will just put a lot of strain on the AV plate, the engine mounts, the tilt tube, and the transom.
 

QBhoy

Fleet Admiral
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Mar 10, 2016
Messages
8,286
What are these pods ? Just when I thought I knew most there is to know ? This is new to me without seeing a picture.
Or is it maybe just an American term for something we have another name for ?
Example....you guys call what we call an auxiliary motor a kicker, haha.
 

Cat nip

Petty Officer 1st Class
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Jul 25, 2015
Messages
288
No Title

Here is the pods. If they dont angle up at the back and stay flush and square with the bottom it will plow.
 

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Sea Rider

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Sep 20, 2008
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Is it possible removing them, chop both dowm to have a clear unobstructed rear hull ? At plane are they producing side splashes, water disturbances. Does water flow exits flat at middlet hull shape ? if flat, flat, if round, round and so on..

Happy Boating
 
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